At what age do children begin to tell lies?

© 2021 GWEN DEWAR, PH.D., ALL RIGHTS RESERVED

Little kids sometimes say goofy things. They sometimes say things that aren’t true. But being goofy or mistaken isn’t the same thing as telling a lie.

As commonly understood, the act of lying requires both insincerity and the intention to deceive. In other words, you have to make a statement that you don’t believe yourself, and you must intend to make someone else accept that statement as true (Primoratz 1984). 

When do children start meeting these criteria?

Studies reveal that some toddlers begin lying before they are two and a half years old. And by the age of four, more than 70% of children lie — at least sometimes.

But the timing varies from one individual to the next, and no, it isn’t a reflection of a child’s moral character. In fact, it may take children many years to achieve a nuanced, adult-like understanding of the morality of telling lies.

Instead, the evidence strongly suggests that kids begin experimenting with lying as a natural consequence of cognitive development.

Closeup of child looking sideways by Big D2112

In particular, lying is connected with a child’s “mind-reading” skills: The earlier that children develop advanced insights into how other people think, the sooner they begin testing their abilities to deceive. 

Research also suggests that lying is related to the development of “inhibitory control,” an executive function that helps us resist our impulses. Young children with higher levels of inhibitory control are more likely to lie.

Here are the details.


Lying is developmentally normal, and here’s how we know

Decades ago, researchers devised a clever method for studying lying in children. It’s called the “temptation resistance paradigm,” but you might also call it the “don’t peek” scenario because it’s designed to tempt kids to sneak a look at a hidden object.

Many experiments in lying have relied on this scenario, so let’s take a look at how it unfolds. 

It begins with a child being invited to play a guessing game. The steps are these:

1. The child sits in a chair with his or her back to an adult. The adult advises the child to keep staring straight ahead. Don’t turn around!

2. Then adult explains that she is going to hold up a toy — where the child can’t see it — and play a sound clue. “The sound clue will help you guess what I have.”

3. The child listens to the sound — which is indeed helpful. For instance, if the toy is a rubber duck, the child hears a quacking sound.

4. After being reminded again not to peek, the child makes his or her guess. If the guess is incorrect, the adult provides more clues until the child is successful.

Researchers have the child play a few rounds of the game, so they can be sure the child understands the routine. And then they introduce an interruption: The adult explains that she must leave the child alone for a minute.

The adult tells the child that they will resume playing the game when she returns. Meanwhile, she’ll place the next toy on a table behind the child. She’ll also play the accompanying sound clue. 

“Don’t peek while I’m gone,” she reminds the child. “When I come back you can guess what the toy is.”

With that, the adult exits, leaving the child alone in a room with a hidden camera.

The sound clue begins to play, but this time it provides irrelevant information – music that is unrelated to the identity of the toy. What does the child do next?

In experiment after experiment, it turns out the same way. Irrespective of age, most children succumb to temptation and sneak a peek. But what’s especially interesting is what happens afterwards, when the adult returns.

The adult questions the child. “Did you turn around? Did you peek to see what it was?

And now we see an age difference. Among the youngest children tested — toddlers under the age of 30 months — most confess after peeking. Only about one third of them tell a lie (Evans and Lee 2013). 

But as children approach their fourth birthdays, the statistic flips. Across multiple studies, more than 70% of these kids lie (Evans and Lee 2013; Lee 2013). In other words, lying isn’t just developmentally normal for a 4-year-old to lie. In certain situations, it’s actually the most common response!

So the rate of lying skyrockets between the ages of two and four. Why? 

It’s probably because children are developing important cognitive skills.

As we’ve seen, telling a lie isn’t the same thing as uttering a falsehood. The would-be liar needs to have the goal of deceiving another person, and be capable of following through. The liar needs to keep track of several different representations of reality at once.

  • the true state of affairs, as the liar believes it to be
  • the false reality that the liar wishes to portray, and
  • the beliefs of the person the liar wishes to fool.

That’s pretty complicated stuff, especially the last item. What’s going on in the mind of the other person?

At absolute minimum, a child needs to judge whether or not the other person is already knowledgeable, and therefore an unpromising target of deception.

In the “don’t peek” experiments, the children who lied must have managed this much. They appear to have reasoned that they could get away with lying because the adult wasn’t in the room to witness their peeking.

So they showed at least a little aptitude for “mind-reading,” or what psychologists call “theory of mind.” They judged that the adult was ignorant about the truth. But there is a lot more to understand about another person’s mind. For instance, how do other people come to hold false beliefs?

That sounds like a crucial thing to understand if you are going to deceive someone, and, as it turns out, it’s an aspect of theory of mind that most young children seem to struggle with.

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We know this based on experiments that present kids with the so-called “false belief task,” a task that asks children to follow the actions of a fictional character.

In the story, the character places a favored object in storage (e.g., a black box), and then leaves the scene. A second character arrives, removes the object, and then squirrels it away in a hiding place (e.g., a white box).

The children are then asked to make a prediction: When the first character returns, where will she look for her object?

Adults and older kids have no trouble answering this question. Clearly, the first character will not know that her object has been hidden. She will look for it in the place where she last left it.

But the youngest children usually report otherwise. They say that the character will look in the new hiding place. It’s as if they are confused about the difference between their own, correct knowledge, and the faulty belief of the character.

Why do young children get mixed up about this? As I  opens in a new windowexplain elsewhere, that’s not entirely clear. Maybe they just aren’t paying enough attention.

But regardless, the experiments report an interesting developmental shift: Whereas relatively few 3-year-olds pass the false belief task, most four-year-olds pass with flying colors.

This led researchers to a hypothesis about lying in children: Maybe the pattern of lying in the “don’t peek” experiments reflects a developmental shift in children’s grasp of false beliefs. The rate of lying skyrockets around the age of four — at the same time that most kids begin to pass the false belief task.

If the hypothesis is correct, then we’d expect an individual’s performance in the “don’t peek” experiment to correlate with his or her theory of mind skills. That’s precisely what researchers have found (e.g., Talwar and Lee 2008; Leduc et al 2017).

There is also evidence that kids are quicker to learn deceptive tactics if they already possess a good understanding of false beliefs. 

In one study, researchers took a group of young children who hadn’t yet shown evidence of lying. Then they provided these kids with opportunities to play a competitive game that required deceptive tactics.

With practice, the preschoolers spontaneously learned to deceive — but the children who learned the fastest were those who had shown a prior understanding of false beliefs (Ding et al 2018).

But perhaps the most compelling evidence comes from a teaching intervention: What happens if we take young children who haven’t yet discovered lying, and coach them in the understanding of mental states and false beliefs?

That’s what Xiao Pan Ding and her colleagues wanted to know. So they conducted an experiment.

Study: Kids begin to tell lies immediately after they develop stronger “theory of mind” skills

The researchers began by recruiting a group of kids who had failed to lie in preliminary tests — 42 children in total, who ranged in age from 34 to 40 months (Ding et al 2015). 

Then the researchers randomly assigned each child to receive one of two types of training:

  • Half the kids were assigned to 6 sessions of instruction in theory of mind
  • The remaining half were assigned to 6 sessions of instruction in concepts unrelated to theory of mind (like Piaget’s conservation of number).
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The theory of mind training was specifically designed to get children thinking about the ways that people can be mistaken or deceived.

For example, in one training task, children were shown a pencil box, and asked to guess what was inside. Pencils? No. When children opened the box to check, they discovered there were no pencils. Then they were asked to make a prediction. If you showed this box, unopened, to someone else, what would he or she think was inside it?

At first, kids tended to predict that other people would (somehow) know the correct answer.

But with discussion and practice, the children began to grasp the nature of false beliefs in others, and, unlike kids in the control group, they ended their 6 sessions of training by passing the false belief task.

The children trained in theory of mind also differed in another, crucial way: During a post-training test of deception, they were far more likely to lie. 

Moreover, the effect was lasting. When the children were tested again, 36 days later, they were still more likely to engage in strategic lying than were the kids in the control group (Ding et al 2015).

So there is good reason to think that advanced theory of mind skills facilitate a child’s ability to lie. Understanding false beliefs might help kids recognize the opportunity to lie. It might help them figure out how to lie effectively (Talwar and Lee 2008).

And theory of mind skills aren’t the only factor. There is also evidence that inhibitory control plays a role in the emergence of lying.

As noted above, inhibitory control is what we use to override our automatic, knee-jerk impulses. It also helps us filter out irrelevant information, and stay focused on our goals.

Such abilities could clearly help the would-be liar. To maintain a lie, children need to monitor their own behavior — make sure that they keep their stories straight, and avoid letting the truth leak out by accident.

Are young children more likely to lie if they possess superior inhibitory control? That’s what researchers found in a couple of “don’t peek” studies: 

Young children with superior inhibitory control were more likely to lie, even after controlling for their chronological age (Talwar and Lee 2008; Evans and Lee 2013; Leduc et al 2017; O’Connor et al 2020).

Experimenting with a new mental toolkit

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So this research leave us with a strong impression about the emergence of lying in young children. It seems to follow naturally after kids develop the necessary cognitive prerequisites.

And that makes sense; it’s like the development of other abilities. Children reach new milestones – discover new powers – and immediately explore them.

After all, the incentives to deceive already exist: Children perceive that they can avoid trouble through deception. They discover they can manipulate people to get what they want. It only remains for them to test the system.

Should we be disheartened by these findings? Disturbed that the development of cognitive maturity goes hand-in-hand with the development of lying?

I don’t think so. This is what growing minds do when they discover new powers. Babies delight in dropping objects from their high chairs once they develop the necessary physical coordination. They observe the effects of gravity, and test our responses. With lying, it’s much the same. As children develop new cognitive skills, they experiment with lying, and test our responses.

There are other parallels, too. A child doesn’t wake up one morning and suddenly find herself competent at a new physical skill. She achieves the milestone in steps, over time. The same is true for cognitive skills, including skills related to deception.

When young children begin to lie, their lies are often unconvincing. For example, those “don’t peek” experiments. If you want to get away with lying, you need to maintain a consistent story. It’s not enough to insist that you didn’t sneak a peek. You also need to pretend that you don’t know the identity of the toy. When asked to guess, you should either insist that you have no idea, or deliberately provide an incorrect answer.

But that’s not what they do. Immediately after claiming that they didn’t peek, they typically blurt out the correct answer. “It’s Barney! It’s Barney the purple dinosaur.” In one study, 90% of 3-, 4-, and 5-year-olds who lied made this fundamental mistake (Talwar and Lee 2002).

Barney-the-dinosaur-by-Themeplus-ccbysa2-min.jpg

That sort of giveaway is called “semantic leakage,” and it probably reflects poor inhibitory control, imperfect theory of mind, or both. 

As children develop better cognitive skills, they experience less semantic leakage. But there are growing pains, as exhibited by this 5-year-old’s response. She seemed to recognize the need to provide her listener with a plausible explanation for making a correct “guess.” But her effort fell short:

“I didn’t peek at it. I touched it and it felt purple. So, I think it is Barney” (Talwar and Lee 2002).

Does this mean your child can’t fool you? I’m afraid not. Researchers have documented many cases during “don’t peek” experiments where particularly savvy children performed perfectly. When the researchers played back video recordings to adults who didn’t know the truth, these observers were unable to tell that the children had lied.

So young children  — particularly young children with strong mind-reading skills and self-control — can sometimes pull the wool over our eyes.  But once again, we shouldn’t view this as disturbing or sinister. They are simply exploring the power of their well-developed psychological abilities.

But what about morality? When do children understand that it’s wrong to tell a lie?

That’s an interesting question, and a tricky one. 

For instance, in one study, researchers presented 4-year-olds and 5-year-olds with various truth-telling and lying scenarios, and asked the children for their opinions. The 4-year-olds didn’t judge lies more negatively than truth-telling. But the 5-year-olds did (Vendetti et al 2019).

So we might  conclude that kids don’t really grasp the “wrongness” of a lie until they are at least 5 years old. But that doesn’t mean that younger children never feel any qualms about lying. It’s possible that some 4-year-olds do experience a certain reluctance to lie, even if they don’t label it as “wrong” or “bad” (He and Qin 2020).

And — more generally — the morality of lying can be a complex, murkey business.  Should you tell your grandmother a polite lie, or be brutally honest, and tell her that you hate the cake she baked for you?  Should you tell a bully where his intended victim is hiding, or tell a fib to protect the innocent? Should you lie about your personal accomplishments — downplay them — in order to be modest?  Should you tell a lie to protect a friend, even if it causes harm to society? Should you lie for the public good, at the cost of causing harm to a friend?

Depending on your personal values and cultural upbringing, you might endorse some or all of these types of lies. And when you were growing up, you had to make sense of it all, and figure out where you stood.

So it isn’t really as simple as learning that “it’s wrong to tell a lie.” Kids must learn to weigh the value of truthfulness against other considerations, like the need to be polite. As I explain elsewhere, this more nuanced understanding of the morality of lying may not begin to emerge until kids are 6 or 7 years old. And kids may not reach adult-like levels of understanding until they are more than 11 years old (Fu et al 2007).

What can we do to encourage kids to tell the truth?

A variety of studies point to the same answer: If we want kids to be honest with us, we need to create an environment that rewards truth-telling.

  • We should show kids that we value honesty by modeling it ourselves, because children are more likely to tell lies if they’ve seen adults do the same (Hays and Carver 2014).
  • When children make difficult confessions, we should praise them for their honest dealings (Lee et al 2014; Ma et al 2018).
  • And, as I explain in another article,  opens in a new windowwe should avoid trying to control children through threats and punishments. When adults take a harsh approach to discipline, children are more likely to tell lies (Talwar and Lee 2011). 

More information about the development of lying in children

To learn more about this fascinating research, check out these Parenting Science articles:


References: At what age do children begin to tell lies?

Broomfield K, Robinson EJ, Robinson WP. 2002. Children’s understanding about white lies. British Journal of Developmental Psychology. 20:47–65.

Ding XP, Wellman HM, Wang Y, Fu G, Lee K. 2015. Theory-of-Mind Training Causes Honest Young Children to Lie. Psychol Sci. 26(11):1812-21.

Ding XP, Heyman GD, Fu G, Zhu B, Lee K. 2018. Young children discover how to deceive in 10 days: a microgenetic study. Dev Sci. 21(3):e12566

Fu G, Xu F, Cameron CA, Leyman G, Lee K. 2007. Cross-cultural differences in children’s choices, categorizations, and evaluations of truths and lies. Dev Psychol. 43(2):278-93.  

Fu G, Heyman GD, Chen G, Liu P, Lee K. 2015. Children trust people who lie to benefit others. J Exp Child Psychol. 129:127-39.

Genyue F, Heyman GD, Lee K. 2011. Reasoning about modesty among adolescents and adults in China and the U.S. J Adolesc. 2011 Aug;34(4):599-608.

Hays C and Carver LJ. 2014. Follow the liar: the effects of adult lies on children’s honesty. Dev Sci. 17(6):977-83.

He TS and Qin L. 2020. On the developmental origin of intrinsic honesty. PLoS One. 15(9):e0238241.

Heyman GD, Sweet MA, Lee K. 2009. Children’s Reasoning about Lie-telling and Truth-telling in Politeness Contexts. Soc Dev. 18(3):728-746.

Lee K. 2013. Little Liars: Development of Verbal Deception in Children. Child Dev Perspect. 7(2):91-96.

Lee K, Talwar V, McCarthy A, Ross I, Evans A, Arruda C. 2014. Can classic moral stories promote honesty in children? Psychol Sci. 25(8):1630-6.

Leduc K, Williams S, Gomez-Garibello C, Talwar V. 2017. The contributions of mental state understanding and executive functioning to preschool-aged children’s lie-telling. Br J Dev Psychol. 35(2):288-302.

Ma F, Heyman GD, Jing C, Fu Y, Compton BJ, Xu F, Lee K. 2018. Promoting honesty in young children through observational learning. J Exp Child Psychol. 167:234-245.

O’Connor AM, Dykstra VW, Evans AD. 2020. Executive functions and young children’s lie-telling and lie maintenance. Dev Psychol. 56(7):1278-1289.

Primoratz I. 1984. Lying and the “Methods of Ethics.” International Studies in Philosophy 16: 35–57.

Santos RM, Zanette S, Kwok SM, Heyman GD, Lee K. 2017. Exposure to Parenting by Lying in Childhood: Associations with Negative Outcomes in Adulthood. Front Psychol. 8:1240.

Talwar V and Crossman A. 2011. From little white lies to filthy liars: the evolution of honesty and deception in young children. Adv Child Dev Behav. 40:139-79.

Talwar V and Lee K. 2011. A punitive environment fosters children’s dishonesty: a natural experiment. Child Dev. 82(6):1751-8.

Wang L, Zhu L, and Wang Z. 2017. Parental mind-mindedness but not false belief understanding predicts Hong Kong children’s lie-telling behavior in a temptation resistance task. J Exp Child Psychol. 162:89-100.

Warneken F and Orlins E. 2015. Children tell white lies to make others feel better. Br J Dev Psychol. 33(3):259-70.

Wimmer H and Perner J. 1983. Beliefs about beliefs: representation and constraining function of wrong beliefs in young children’s understanding of deception. Cognition. 1983 Jan;13(1):103-28.

Williams S, Moore K, Crossman AM, Talwar V. 2016. The role of executive functions and theory of mind in children’s prosocial lie-telling. J Exp Child Psychol. 141:256-66.

Content of “At what age do children begin to lie” last modified 9/2018

Closeup image of child looking sideways by Big D2112 /flickr/ ccbynd2

image of false belief task from Wimmer and Perner 1983

image of smiling toddler girl by Marc Davis / flickr / ccby2

image of smiling toddler boy by rashida s. mar b. / flickr/ ccbysa

image of Barney by Themeplus / flickr/ ccbysa2

content last modified 9/2021