Understanding that people can believe something untrue
Most children come to understand that someone can believe something that isn't true somewhere between about 3 and 6 years, often around 4 to 5. In five very different countries, about half of 4-year-olds and most 5-year-olds understood it.
How sure are we?
Fairly sure. Studies in eight countries agree, but they all tested children the same way, with simple acting-out games. How we know this
What it’s a sign of
Your child is learning that what people do depends on what they believe, even when it's wrong, which helps with understanding others, surprises and secrets.
Some lab studies found signs of this in babies of about 15 months, from where they look. Several careful attempts to repeat studies like these didn't get the same results, so researchers disagree about babies. The ages here are for the simple game where a child says or points to where someone will look.
We haven't yet read the large study that pulled together 178 earlier studies by age. We don't know the age by which nearly all children understand this.
A main source for the ages
Synchrony in the Onset of Mental-State Reasoning
Tara C. Callaghan, Philippe Rochat, Angeline Stoll Lillard, Mary Louise Claux, Hal Odden, Shoji Itakura, Sombat Tapanya, Saraswati Singh · 2005 · Psychological Science
- Children
- About 270 children
- Where
- Canada, Peru, Samoa, India and Thailand
- Ages
- 2½ to 6 years
- How
- Researchers tested each child once with the same simple hiding game
- What it found
- About 1 in 7 three-year-olds, half of four-year-olds and more than 8 in 10 five-year-olds understood that someone would look where she wrongly believed a toy was. The age was similar in all five countries.
- Limits
- Some children's ages had to be estimated because birth dates weren't recorded. Only one task was used.
A main source for the ages
Sequential Progressions in a Theory-of-Mind Scale: Longitudinal Perspectives
Henry M. Wellman, Fang Fuxi, Candida C. Peterson · 2011 · Child Development
- Children
- About 400 children
- Where
- The United States, Australia and China
- Ages
- About 3 to 6 years
- How
- Researchers tested children with five short story tasks
- What it found
- Children learned these ideas in the same order. Children whose only success was knowing that people like different things were about 3½ on average; those who also understood untrue beliefs were about 5.
- Limits
- These are average ages of children at each step, not the age when half of children get there. It pools earlier studies by the same research group.
A main source for the ages
Meta-Analysis of Theory-of-Mind Development: The Truth about False Belief
Henry M. Wellman, David Cross, Julanne King Watson · 2001 · Child Development
- Children
- Children from 178 studies
- Where
- Several countries
- Ages
- Preschool years
- How
- A study that pulled together lots of studies
- What it found
- Across 178 studies and several countries, children went from mostly wrong to mostly right answers during the preschool years, whatever version of the task was used.
- Limits
- We have only read the summary; the ages by year are in the paper's figures, which we haven't yet read.
A study that questioned earlier findings
Do 15-Month-Old Infants Understand False Beliefs?
Kristine H. Onishi, Renée Baillargeon · 2005 · Science
- Children
- About 60 babies
- Where
- A lab in Illinois, United States
- Ages
- About 15 months
- How
- Researchers measured how long babies looked at different scenes
- What it found
- Babies looked longer when an actor searched where she couldn't know the toy was, which the authors read as early understanding of untrue beliefs.
- Limits
- Reports group results only. Later attempts to repeat studies like this often failed.
A study that questioned earlier findings
Is Implicit Theory of Mind a Real and Robust Phenomenon? Results From a Systematic Replication Study
Louisa Kulke, Britta von Duhn, Dana Schneider, Hannes Rakoczy · 2018 · Psychological Science
- Children
- Not given in the summary we read
- Where
- Not given in the summary we read
- Ages
- Not given in the summary we read
- How
- Researchers repeated earlier studies with their original materials
- What it found
- Only one of four well-known looking tasks gave the same result again, and that one stopped working once other explanations were ruled out.
- Limits
- We have only read the summary. It tested a different kind of looking task from the 15-month study.
If you’re worried about your child, talk to your child and family health nurse or GP.
Last checked 2 November 2026