Cognitive flexibility is a sophisticated form of executive functions that predicts a range of adaptive outcomes; however, little is known about which caregiving behaviors predict the rapid improvements in children's cognitive flexibility during early childhood. This study examined whether ordinary variations in mothers' provision of emotional and cognitive support during problem-solving predict children's cognitive flexibility and tested whether children's cognitive flexibility predicts caregiving behaviors across time. Two hundred and seventy-eight children and their caregivers (96% mothers) participated in laboratory visits when children were in preschool, kindergarten, and first grade. At each visit, cognitive flexibility was measured via a computerized version of the Dimensional Change Card Sort task and mothers' behaviors were observed during a semi-structured problem-solving board game task. Results from autoregressive cross-lagged structural regression analyses indicated that mothers' emotional support predicted greater child cognitive flexibility from preschool to kindergarten, and from kindergarten to first grade, after accounting for the stability in these constructs over time and controlling for the influence of maternal education, and child age and minority status. Mothers' cognitive support did not predict child cognitive flexibility over time. Child cognitive flexibility did not lead to changes in caregiving behaviors over time. Findings suggest that mothers' provision of emotional support during problem-solving may be an important proximal mechanism that contributes to children's cognitive flexibility across early childhood.