Every parent knows that toddlers are strange and inscrutable creatures. They are capricious and contradictory, particularly when trying to interact with other people. My two-year-old daughter is no exception. One moment she is worrying about a crying baby. The next, she is snatching away her friend’s toy and shouting, “Mine!” When I tell her not to do something, it feels like I’m talking to a brick wall. Yet a new study suggests that what I say to her today could shape her ability to reason about other minds for years to come.

For decades, scientists believed that theory of mind – the ability to reason about other people’s thoughts and emotions – doesn’t begin to mature until children reach the age of three or four. They came up with this age using a test called the false-belief task. The test probes whether a child can take the perspective of someone else. In one classic example, children are presented with the following scenario: Sally is playing with a ball. She puts it in a basket and leaves. While she’s gone, Anne moves the ball from the basket to a box. The child is then asked: “When Sally returns, where will she look for the ball?“

Most two- and three-year-olds answer that Sally would look in the box because that’s where they know the ball is. But by four or five, children typically say that Sally would look in the basket because that’s where she would think the ball is. It is a simple switch from an answer based on concrete facts to one based on presumptions about someone else’s knowledge or beliefs. Yet this modest development allows us to survive and thrive in an interconnected, social world. From office collaborations to divvying up chores and even navigating a busy traffic intersection, we rely on our ability to surmise the thoughts of others. How else could we predict what they are likely to do next?

While children’s performance on the false-belief task initially led scientists to conclude that theory of mind develops around age four, that assumption has since been overturned. Beginning in 2005, a series of clever studies found evidence of theory of mind in toddlers and even infants as young as ten months of age. These studies used modified versions of the false-belief task that measured children’s expectations nonverbally. For instance, since infants look longer at events that surprise them, developmental psychologists can use gaze time to infer the predictions of preverbal children. In modified versions of the false-belief task, toddlers and infants stared longer when someone searched for an object where it actually was, rather than where that person would have expected the object to be.

While children typically master the standard false-belief task around the age of four, the timing can range from three to nearly six years of age, depending on the child. Parent-child interactions seem to factor into the timing of this milestone in individual children. Studies have shown that when mothers refer more often to mental states (thoughts, emotions, and desires) in conversations with their young children, these children tend to perform better on theory of mind tests a few years down the line. But is this effect just a matter of learning a few keys words a little sooner or can it lead to long-lasting differences in theory of mind ability?

Rosie Ensor, Claire Hughes, and their colleagues at University of Cambridge tackled this question by testing children over the course of eight years. They first visited the homes of two-year-olds during a family meal and recorded how often the mother and child used ‘thought words’ such as know, forget, think, idea, interest, and understand. One year later, they administered standard false-belief tests and a verbal comprehension test to each child. About three years after that, they gave the kids more false-belief tests and also recorded how often the mothers and children used ‘thought words’ when they read a picture book at home together. Four years after that, when the children were ten and eleven, they administered another verbal comprehension test and ran the children through a different theory of mind test called the Strange Stories. Finally, the authors studied the correlations between these measures and modeled their relationships to one another.

The scientists published their results recently in the journal Child Development. They found that the number of times mothers used ‘thought words’ with their two-year-olds predicted the children’s performance on theory of mind tests at six and ten years of age. The effect wasn’t a reflection of language mastery or the fact that mothers who use many ‘thought words’ with toddlers will tend to do the same when their children are older. Neither the children’s verbal comprehension scores nor the mothers’ use of ‘thought words’ with their children at age six could account for the results.

Will talking to a two-year-old about others’ thoughts and beliefs make a child better at social reasoning down the line? It’s hard to say. These latest results are based on correlations and can’t prove that one thing causes another. Still, they are intriguing and suggestive. Encouraging young children to think about others’ beliefs and feelings may strengthen theory of mind abilities or simply get children into the habit of considering others’ thoughts in ways that persist into their middle-school years.

It’s even possible that the effect lasts beyond the tween years. We all know adults who don’t seem to understand or consider the thoughts and feelings of others. A recent study confirmed that adults differ in their ability to reason about other people’s mental states. It may be that the early discussions we have with children about thoughts and feelings – even before we realize that they are listening – can set the stage for subtle differences in this type of reasoning into adolescence and even adulthood.

For now, it’s clear that a toddler’s understanding of other minds is a complex and evolving landscape. I see it everyday in the kindnesses and cruelties of my daughter. The world is a social labyrinth that she must learn to navigate as she grows and gains her independence. But maybe, by talking about thoughts and beliefs with her today, I can prepare her and give her the tools she’ll need to find her way tomorrow.

Are you a scientist who specializes in neuroscience, cognitive science, or psychology? And have you read a recent peer-reviewed paper that you would like to write about? Please send suggestions to Mind Matters editor Gareth Cook, a Pulitzer prize-winning journalist and regular contributor to NewYorker.com. Gareth is also the series editor of Best American Infographics, and can be reached at garethideas AT gmail.com or Twitter @garethideas.