Children vary in how sensitive they are to experiences, with consequences for their developmental outcomes. In the current study, we investigated how behavioral sensitivity at age 3 years predicts mental health in middle childhood. Using a novel repeated measures design, we calculated child sensitivity to multiple psychological and social influences: parent praise, parent stress, child mood, and child sleep. We conceptualized sensitivity as the strength and direction of the relationship between psychosocial influences and child behavior, operationalized as toothbrushing time, at age 3 years. When children were 5-7 years old (n = 60), parents reported on children's internalizing and externalizing problems. Children who were more sensitive to their parents' praise at age 3 had fewer internalizing (r = -0.37, p = 0.016, p[subscript FDR] = 0.042) and externalizing (r = -0.35, p = 0.021, p[subscript FDR] = 0.042) problems in middle childhood. Higher average parent praise also marginally predicted fewer externalizing problems (r = -0.33, p = 0.006, p[subscript FDR] = 0.057). Child sensitivity to mood predicted fewer internalizing (r = -0.32, p = 0.013, p[subscript FDR] = 0.042) and externalizing (r = -0.38, p = 0.003, p[subscript FDR] = 0.026) problems. By capturing variability in how children respond to daily fluctuations in their environment, we can contribute to the early prediction of mental health problems and improve access to early intervention services for children and families who need them most.