Kindred spirits

Abstract

Two experiments were conducted to examine the development of a theory of mind in 265 children aged 3 to 5 years from families of varied size. Even after verbal mental age was controlled, those who had a sibling aged 12 months to 12 years outperformed only-children in both experiments. However, the presence of a very young infant, or of siblings who were teenagers or young adults, exerted no benefit. Also, in contrast to some previous studies, younger child siblings and twins were just as helpful as older child siblings. The presence of multiple child siblings of varied ages above and below that of the participant predicted advanced theory of mind development over and above the effects of own age and verbal ability, despite the fact that neither overall family size nor birth order were significant predictors. These findings were reconciled with those of previous sibling constellation research around a model of family social influences in which the opportunity to play, converse, and disagree in distinctively childish ways with brothers and sisters provides unique insights into the workings of the human mind.