Several decades of research have concluded that child social functioning is a critical predictor of wellbeing across various developmental domains. Most scientists agree that both genetic and environmental influences play defining roles in social behavior; the processes by which they concurrently affect child development, however, has been the subject of less research. This work examines distinct mechanisms that shape child prosociality by examining genetic and environmental influences on development, via two empirical studies. The first study analyzed the evocative-reactive and the evocative-socially-mediated hypotheses as gene-environment correlation (rGE) mechanisms connecting the arginine vasopressin receptor 1a (AVPR1a) and dopamine receptor D2 (DRD2) genes, child prosocial behavior, and parent differential treatment (PDT). Findings present modest evidence for the evocative-reactive rGE hypothesis; specifically, AVPR1a marginally influenced child prosociality, which subsequently predicted mother preference in adolescence. The second study examined several gene-environment interactions (GxEs) in exploring how social environmental variables- positive and negative parenting- predicted child prosociality, as moderated by socially-implicated child genes, DRD2 and dopamine receptor D4 (DRD4). Findings indicated that while positive parenting was predictive of child prosociality regardless of genetic variants, the effects of negative parenting on child prosociality were dependent on child genetic variants. Together, findings from these studies suggest modest genetic and environmental influences on child behavior in middle childhood and adolescence, consistent with previous research and theory. Directions for future research are offered, and intervention and policy implications are discussed.