Developmental associations between poor executive function (EF) and problem behaviors in toddlerhood indicate that the interplay between cognition and affect begins very early in life (Hughes, Devine, Mesman, & Blair, 2020). However, very few longitudinal studies of toddlers have included direct measures of both EF and emotion regulation (ER). In addition, while models of ER highlight the importance of situational contexts (e.g., Miller, McDonough, Rosenblum, Sameroff, 2005), existing work is limited by a heavy reliance on lab-based observations of mother-child dyads. Addressing these twin gaps, the current study of 197 families included video-based ratings of ER in toddlers' dyadic play with both mothers and fathers at each of two time-points (14- and 24-months), with parallel measures of EF being gathered in each home visit. Our cross-lagged analyses showed that EF at 14 months predicted ER at 24 months, but this association was limited to observations of toddlers with mothers. It was also asymmetric: ER at 14 months did not predict EF at 24 months. These findings support co-regulation models of early ER and highlight the predictive utility of very early individual differences in EF.