Theory of mind in 3 to 5 year olds | MyOwnChildbook
Ask your three-year-old where Daddy hid the biscuits, and she will answer immediately - even though she was not there when he hid them. This is not cleverness. It is the absence of theory of mind, and it is completely normal for toddlers.
Theory of mind is the ability to understand that other people can hold thoughts, beliefs and knowledge that differ from your own. Research by Austrian psychologists Heinz Wimmer and Josef Perner, published in the scientific journal Cognition (1983), was the first to demonstrate experimentally that children acquire this ability around their fourth year of life. The study has since been replicated hundreds of times worldwide and remains one of the most cited findings in cognitive developmental psychology.
The Sally-Anne test: how scientists discovered it
The classic experiment that Wimmer and Perner designed - later refined into the Sally-Anne test by Baron-Cohen, Leslie and Frith (1985) - works like this: two dolls, Sally and Anne, play together. Sally puts a marble in her basket and leaves the room. Anne picks up the marble and moves it to a box. Then Sally comes back.
The question: “Where will Sally look for her marble?”
Children under four almost always answer: in the box, where the marble actually is now. They do not yet grasp that Sally can hold a false belief - that Sally will look in the basket, because that is all she knows. Children between four and five begin to understand that Sally’s knowledge differs from reality, and that she will search where she believes the marble to be.
Wimmer and Perner tested 106 children and found a significant shift in understanding between ages three and five. The core finding: before age four, children assume that everyone sees the world the way they see it.
The four developmental steps
A meta-analysis by Wellman, Cross and Watson, published in Child Development (2001) - reviewing 178 individual false belief studies - confirmed that theory of mind development follows a consistent sequence, regardless of culture or parenting style:
- Understanding that others can have different desires (18-24 months)
- Understanding that others can have different knowledge (2-3 years, emerging but not yet stable)
- Understanding false beliefs - someone can believe something that is wrong (3-4.5 years: the major leap)
- Understanding hidden emotions - someone can feel differently than they show (4-6 years)
The third step is the most significant. It is the moment when a child grasps: what I know, someone else may not know. And what someone else believes does not have to be true.
Why this surprises parents
Parents often experience this transition as a sudden improvement in empathy. “She suddenly asks how I am when I look sad,” is a typical observation. Or a child begins to understand why a surprise needs to be kept secret. Before age four, the concept of a “surprise” literally makes no sense to a child: in their mental model, everyone knows what the present is once you do.
The same cognitive leap makes stories richer. Children who have developed theory of mind can follow plot tensions: the hero knows something the villain does not. They can feel for a character who is mistaken. They begin to understand irony - saying one thing and meaning another.
Before this phase, a complex plot involving deception, secrets and surprises is largely noise for a child. The story gets followed, but not truly experienced.
What this means for stories and personalisation
This is where it becomes relevant for parents thinking about which books to offer their child. Before the third phase - below roughly ages three to four - a complex storyline lands poorly. Books with repeating phrases, predictable structure and strong contrasting colours do more at that age. The reason toddlers want the same book read dozens of times is partly connected to this: the unsurprising is pleasant and safe. Read more about that phenomenon in our post on why children want the same book read a hundred times.
Once a child has made the false belief leap, the nature of enjoyment in stories shifts. A personalised children’s book with their own name - where they are the hero discovering something the other characters do not yet know - connects directly to that cognitive reality. The child now understands: I know something that others do not. That transforms a story from something followed into something lived.
When development takes a different path
Theory of mind does not develop on the same schedule for every child. In children on the autism spectrum, the third step - understanding false beliefs - often unfolds differently or later. Baron-Cohen et al. (1985) showed that autistic children more frequently “fail” the Sally-Anne test than neurotypical peers, not because of lower intelligence, but because social-mental inference is structured differently for them.
For parents of children on the autism spectrum: the absence of typical theory of mind responses says nothing about a need for connection and stories. That need is present, but the route is different. A book about something the child genuinely experiences - their own name, their own animals, their own familiar place - can resonate deeply even without a complex plot. The recognition (“that is me!”) works independently of theory of mind.
When plots and deception do not yet land, classic picture books built on emotional recognition and repetition are a strong alternative - books structured around familiarity rather than cognitive complexity. And there are situations where a personalised book simply is not the right choice: for an honest guide to those, read when a personalised book does not fit.
Knowing more than everyone around you
Theory of mind is not a developmental milestone that simply passes and is forgotten. It is the foundation for empathy, social understanding and the ability to step into another person’s shoes - capacities children draw on for a lifetime.
A parent who understands which step their child is navigating can offer stories that connect at exactly that point: repetition and predictability for the toddler who still sees the world as a shared panorama, and later an adventure as the hero for the child who has discovered that they know more than the other characters in their story.