Siblings at home: Moderating influence of sibling presence and composition on the relation between problem behaviors and Theory of Mind in early childhood.

Despite the prevalence of internalizing and externalizing difficulties in children, the impact of these problem behaviors on the development of important social cognitive skills, such as Theory of Mind (ToM), is not well-understood. Indeed, many studies that have explored relations between problem behaviors and ToM report inconsistent findings. A possible reason for these disparities may be a lack of accounting for social protective factors within the home, such as the presence and number of siblings. Here, we explored the moderating influence of sibling presence and number on the relation between problem behaviors (i.e., internalizing and externalizing) and ToM. A total of 184 children (88 boys; M = 64.6 months, SD = 10.39) completed six well-validated ToM tasks while mothers reported on their children's externalizing and internalizing behaviors. Children who had siblings living in the same home exhibited higher ToM than children without siblings. In addition, both sibling presence and number of siblings moderated the relation between children's externalizing behaviors and ToM, such that in children without siblings externalizing behaviors were negatively associated with ToM. In contrast, children with siblings had similar ToM regardless of externalizing behaviors. As well, children with relatively fewer siblings and higher externalizing behaviors displayed lower ToM than children with relatively more siblings and higher externalizing behaviors. We did not detect a moderating effect of sibling presence or number on the relation between internalizing behaviors and ToM. These findings provide support for siblings' protective utility within the context of children's social cognition.