Maternal depressive symptoms (MDS) are inconsistently associated with lower rates of child prosocial behavior. Studies typically examine prosocial behavior as a unitary construct rather than examining its multiple dimensions, and rarely consider how the quality of the parent-child relationship could influence this association. The current study examines whether the security of the parent-child attachment relationship moderates the association between MDS and children’s helping, sharing, and comforting behaviors. Participants were 164 low-income, majority African American mothers and their preschool-aged children recruited from Head Start centers. Mothers reported the frequency of depressive symptoms at baseline; child attachment security and helping, sharing, and comforting behavior were observationally assessed 5 to 8 months later. Moderation analyses revealed a positive main effect of security (but not MDS) on children’s comforting behavior, a main effect of MDS on sharing, and no main effects of MDS or security on children’s helping behaviors. Significant interactions between MDS and security predicted comforting and (marginally) helping behaviors, such that MDS were associated with both more helping and more comforting behavior only when children were more secure. No such interaction was observed for sharing. These findings suggest that children may adapt to maternal depressive symptoms in prosocial ways, but that this depends at least in part on the quality of the parent-child relationship, underscoring the importance of examining attachment quality as a moderator of parental influences on children’s social-emotional development. We discuss potential explanations for these findings, as well as their implications for intervention.