Research has identified antecedents to flourishing--high levels of social, emotional, and psychological health--in adolescence and adulthood but few studies have attended to flourishing in childhood. Moreover, although there has been great interest in how environmental effects on mental illness vary by temperament, little attention has been devoted to the possibility that children with internalizing disorders are more sensitive to social ecology in terms of their mental "health." This study tested these possibilities using national data from children aged two to five (n = 19,957). Findings indicate parental investment and negative parental regard predicted greater and lesser flourishing, respectively, and the effect of negative parental regard on flourishing was significantly larger among children with internalizing disorders. Taken together, results suggest interventions may promote mental health via special attention to the social ecology inhabited by children experiencing internalizing problems.