Social mastery motivation and parental response are important correlates of children's vocabulary and self-regulation skills, but little research has examined their relationships collectively. This study investigated the direct relationships among social mastery motivation (active interaction and positive affect frequencies), parental response, and self-regulation skills and the indirect relationships via vocabulary knowledge. Participants were 182 Hong Kong children (83 girls, mean age 3.82) and their parents. Path analysis revealed that active interaction frequency had direct negative (in boys) and marginal indirect positive relationships (via vocabulary knowledge, in girls) with self-regulation, whereas positive affect frequency was indirectly related to boys' self-regulation through expressive vocabulary. Parental response was positively related to self-regulation and marginally to social mastery motivation in boys only. Findings highlight that different aspects of social mastery motivation may relate to boys' and girls' vocabulary and self-regulation skills, and that parental response may particularly shape boys' social mastery motivation and self-regulation.