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"Little liars": Babies can understand deception before their first birthday, new research suggests

"Little liars": Babies can understand deception before their first birthday, new research suggests

A study of 750 children found some babies recognise deception as early as eight months old.

Two young sisters covering their faces with their hands, playing hide and seek

Published: March 16, 2026 at 1:13 PM

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You might not expect your children to be lying to you before they can even talk. But babies may be picking up the basics of deception far earlier than many parents realise.

A new international study led by the University of Bristol has found that some children can recognise deception before their first birthday, with many beginning to practise sneaky behaviour during their toddler years. Researchers say the findings offer reassuring insight for parents, showing that early trickery is a normal part of development.

The study mapped how children learn to understand and use deception from birth to age four, and suggests that what might look like cheeky behaviour is actually part of learning about language, social relationships and how other people think.

Some babies recognise deception before age one

Researchers surveyed the parents of more than 750 children aged between 0 and 47 months in the UK, US, Australia and Canada.

Their responses revealed that around a quarter of children appear to understand deception by 10 months old, rising to half by 17 months. Some parents even reported their babies recognising the concept as early as eight months.

The team also found that once children begin using deception, it tends to happen often. Among children reported as deceivers, around half had done something sneaky within the previous day.

Study lead author Elena Hoicka, Professor of Education at the University of Bristol, said it was striking how early these behaviours appeared.

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’.

Elena Hoicka, Professor of Education at the University of Bristol

“Previous research has often focussed on deception as something very sophisticated requiring strong language skills and an advanced understanding of others’ minds. By considering how deception occurs in animals, including chimpanzees, capuchin monkeys, antelopes, and birds, and applying this to young children, we were able to document the first much earlier forms of deception in young children – and it would seem to start very early on indeed.”

The sneaky behaviours toddlers often try

By analysing parents’ answers, researchers identified 16 different types of deception used by young children.

From around age two, these behaviours are usually action-based or rely on very simple speech.

According to Professor Hoicka, common examples include pretending not to hear when a parent says “time to tidy up”, hiding things, or denying something they clearly did.

“It could also extend to doing forbidden activities in secret, for example looking in a bag they were told not to look in when no one is apparently watching or making excuses, such as claiming to need the toilet when asked to tidy up,” she explained.

The behaviours might sound familiar to many parents. Professor Hoicka joked that her own children have their own creative strategies.

As a mother of three children myself, I can certainly vouch for how artful and wily they can be. Hiding under the table or in the bathroom to eat sweets or chocolate is their common ploy.

Elena Hoicka, Professor of Education at the University of Bristol

By age three, children become more creative

The study found that by the age of three, children typically begin experimenting with more complex forms of deception.

At this stage, their growing language skills and understanding of other people’s thoughts allow them to try more elaborate tactics.

Professor Hoicka said this can include exaggeration, understatement or complete fabrication.

“This could mean exaggerating, such as saying ‘I ate all my peas’ when they only ate a quarter, understatement or indeed complete fabrication such as telling a lie like ‘a ghost ate the chocolate’, as well as pretending not to know, see, or understand,” she said.

Children also begin to learn how to leave out key details or redirect attention.

“They also start to withhold information, for instance accurately telling their parents their sibling hit them, while leaving out the fact that they hit their sibling first. Three-year-olds also start to use distraction, like telling someone to ‘Look over there!’ when they want to do something they’re not supposed to.”

Why deception can be a normal part of development

While hearing that toddlers can lie might sound worrying, researchers say the findings should reassure parents.

Understanding deception requires children to recognise that other people have their own thoughts, beliefs and knowledge. Psychologists often view this as an important milestone in social and cognitive development.

Professor Hoicka said the study can help parents know what to expect as their child grows.

She explained that recognising the different stages may help parents respond calmly and guide children towards honesty.

“Firstly, parents can be reassured deception is entirely normal in toddler development. They can also look at our findings to know which types of deception to expect by age, so they can better understand and communicate with their children in order to stay one step ahead of their deceit.”

What the research means

The research also caught the attention of philosophers who study honesty and lying.

Study co-author Jennifer Saul, Professor of Philosophy at the University of Waterloo and author of the book Lying, Misleading, and What is Said, said the findings show that deception develops far earlier than traditionally assumed.

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

For parents of curious toddlers, the message is simple. That cheeky denial about the missing biscuit might not just be mischief, it could be an early sign that their child is learning how the social world works.