Theory of Mind Is Contagious: You Catch It from Your Sibs

This study investigated the relation between family size and ''theory of mind.'' Results from an experiment with 3- and 4-year-olds showed that children from larger families were better able than children from smaller families to predict a story character's mistaken (false-belief based) action. Results from a second experiment on children with exactly 1 sibling failed to show any superiority of older over younger siblings in promoting earlier understanding of belief. The data are interpreted as suggesting that sibling interaction provides a rich ''data base'' for building a theory of mind, and this is discussed in relation to other studies showing that particular kinds of interaction between sibling and child, or caregiver and child, have a beneficial effect on the understanding of false belief.