Sibling relationship quality from birth to adolescence: the enduring contributions of friends.

The purpose of the present study was to examine continuity in sibling relationships across childhood and to evaluate the degree to which children's experiences with their friends and mothers prior to their sibling's birth predict the quality of the relationship they establish with their siblings in adolescence. Twenty-eight firstborn children, who were 48 months old at the time of their sibling's birth, were observed interacting with their siblings and friends at multiple time points. The level of positive social behaviors demonstrated in their early relationships with friends continued to predict sibling relationship quality in adolescence. Firstborn children who had more positive interactions with friends prior to their sibling's birth demonstrated more prosocial interactions with both their siblings and friends in adolescence and exhibited fewer externalizing behaviors. Longitudinal associations support the hypothesis that the social competencies that young children demonstrate in their early relationships with friends may have enduring significance for their social development.