The transition to adolescence is a critical phase for shaping child behavior. Previous studies have revealed the correlation between perceived social support and children’s social behaviors. However, the longitudinal causal relationship between perceived social support and social behavior remains unclear. This study aimed to reveal the longitudinal, bidirectional relationship between perceived social support (from parents, peers, and teachers) and social behaviors (i.e., prosocial behavior, aggressive behavior, and social withdrawal) and the potential mediating role of social self-concept. 577 Chinese children in preadolescence and early adolescence participated in the study at three time points. Results indicated that prosocial and aggressive behavior predicted subsequent perceived social support from peers and teachers. Social withdrawal negatively predicted subsequent perceived social support from parents, peers, and teachers. In turn, only perceived peer support marginally and negatively predicted subsequent aggressive behavior. Social self-concept mediated the effect of social behaviors on perceived social support, the effect of perceived parent support on social behaviors, and the effect of perceived peer support on negative social behaviors. No significant difference was found in the above associations between children in preadolescence and early adolescence. The study highlights the significance of children’s self-evaluation and self-cognition in promoting their perceived social support and adjusting their social behaviors, which provides implications for family- and school-based education and interventions.