The present study examined the interplay among negative emotionality, responsive parenting and socio‐cognitive developmental outcomes (i.e., communication, personal‐social and problem‐solving outcomes) in about 1620 Korean children using three waves of longitudinal data spanning the first 2 years of their life. Results from the Structural Equation Modeling (SEM) demonstrated that there were moderate to low degrees of stability in negative emotionality, responsive parenting and socio‐cognitive developmental outcomes from infancy to toddlerhood. Evidence for reciprocity in the parent–child relationship was found; responsive parenting predicted higher levels of subsequent child communication (in infancy and toddlerhood), and infants' higher problem‐solving ability predicted higher responsive parenting in toddlerhood. Overall, the cross‐age associations among the variables were similar between boys and girls, but some different patterns were observed: when controlling for family contextual factors and the within‐time correlations, negative emotionality at an earlier point significantly predicted lower responsive parenting at a later point and vice versa only in girls during infancy, but neither in boys nor in toddlerhood. The implications of these findings are discussed. Copyright © 2016 John Wiley & Sons, Ltd.