Babies understand deceit as early as 8 months old. By age 3, children are adept ‘little liars’

About 1 in 4 infants are beginning to understand the concept of deception at 10 months old, and that ratio jumps to 50% at 17 months, the study found. By the time children are 3 years old, they often lie more frequently and are more elaborate in their attempts at trickery. 

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The study, published in the medial journal Cognitive Development, is based on interviews researchers conducted with the parents of 750 children up to nearly 4 years old. 

In some cases, parents reported that their children had started showing signs of deceit by 8 months. The earliest versions of deception included hiding items and pretending not to hear. 

Once children began lying, deception became more frequent, researchers found. More than 50% of parents whose children had begun dabbling in deception said their kids had “done something sneaky” within the past 24 hours.

At age 2, deception typically was limited to basic actions and responses — like pretending not to hear instructions to clean up, waiting until no one is looking to do something wrong or denying doing something to avoid consequences.

But by 3, children showed a deeper understanding. They may exaggerate, withhold information or intentionally distract adults when they want to do something they’ve been told not to do. They also may pretend not to see or understand something, and their lies may become more elaborate. 

Previous research has viewed deception as a sophisticated concept that requires strong language skills and an understanding of others, said Elena Hoicka, a professor of education at the University of Bristol in England and the lead author for the study. 

Elena Hoicka, a professor of education at the University of Bristol and lead author for the study, said that previous studies viewed deception as a sophisticated concept which required strong language skills and understanding of others. The new study calls that into question.

“It was fascinating to uncover how children’s understanding and usage of deception evolves from a surprisingly young age and builds in their first years so they become quite adept and cunning ‘little liars,'” Hoicka said in a news release. 

The study suggests that early signs of lying are normal for toddlers, Hoicka said. Understanding the type of deception that children engage in at various ages can help parents better understand their children and communicate how to avoid deception in the future. 

Jennifer Saul, the study’s co-author and a professor at the University of Waterloo in Canada, noted the findings bring a new perspective to the philosophy behind lying and deception. 

“Philosophers have long reflected on the morality of human deception, but always focused on adults deceiving one another,” Saul said. “This study shows just how much complexity gets overlooked by that focus.”