Infant twins’ social interactions with caregivers and same-age siblings

•Development of twins’ social engagement is consistent with singletons’.•Infant–mother social interactions are more sophisticated than between twin siblings.•Engagement states between twin siblings consist of less overtly social behavior.•Twins socially interact more with expert partners over equally familiar novices.•Coordinated joint activity requires an expert partner's scaffolding through 2nd year.

The study of twin behavior offers the opportunity to study differential patterns of social and communicative interactions in a context where the adult partner and same-age peer are equally familiar. We investigated the development of social engagement, communicative gestures, and imitation in 7- to 25-month-old twins. Twin dyads (N = 20 pairs) participated in 10-min, semi-structured play sessions, with the mother seated in a chair completing paperwork for half the session, and on the floor with her children for the other half. Overall, twins engaged more with their mothers than with their siblings: they showed objects and imitated speech and object use more frequently when interacting with their mothers than with their siblings. When the mother was otherwise engaged, the twins played with toys separately, observed each other's toy play, or were unengaged. These results demonstrate that adult scaffolding of social interactions supports increased communicative bids even in a context where both familiar peers and adults are available as communicative partners.