Positive parenting behaviors and children's internalizing problems (Int. Probs) are bidirectionally associated during late childhood and early adolescence. These bidirectional associations likely emerge earlier and may be stronger when children are prone to reactive negative emotions, making parents' support especially critical in children's regulation of negative emotions. The purpose of this study was to test (a) bidirectional associations between parents' positive responsivity and children's internalizing problems from very early through middle childhood and (b) the moderating role of children's negative emotionality in these bidirectional associations (N = 4,898). Small bidirectional associations between internalizing problems and responsivity were found from ages 3 to 5. Internalizing problems at 3 years were negatively associated with responsive parenting at 5 years. Parent responsivity at 3 and 5 years was negatively associated with later internalizing problems at ages 5 and 9 years, respectively. Negative emotionality only moderated the parent-driven association between responsivity at 3 years and internalizing problems at 5 years, with higher responsivity associated with lower internalizing problems only for children with moderate to high negative emotionality. Parents' positive responsivity to children's behavior and children's internalizing problems were only bidirectionally associated in early childhood (ages 3-5). Across ages 3-5 and 5-9, greater parent responsivity to children's behavior was associated with fewer internalizing problems and may be especially beneficial for children with higher negative emotionality. Results further suggest that young children experiencing internalizing problems may be more likely to receive less responsive parenting later, regardless of children's negative emotionality. (PsycInfo Database Record (c) 2025 APA, all rights reserved).