We investigated the role of intra-familial and extra-familial relationships in children’s and adolescents’ prosocial behavior. Due to the changing quality of family relationships in the process of growing up, we compared two developmental stages: middle childhood and middle adolescence. For intra-familial relationships, we assessed the affective relationship quality and the communicative quality between parents and within the parent-child dyad. For extra-familial relationships, we measured parental work experiences and the presence of social networks. Analyses are based on the data from two collection waves (2006, 2007) of the youngest cohort (6-year olds) and the middle cohort (15-year olds) of the Swiss Survey of Children andYouth (COCON). The results reveal that the relationship quality between parents predicts children’s prosocial behavior, whereas the communicative quality of the parent-child dyad is more important in adolescence. Parental work experiences and social networks predict prosocial behavior indirectly through the quality of affective relationships and the quality of communication within the family.