This study examines the association between teacher--child interaction quality and children's self-regulation in Finnish and Portuguese toddler classrooms. The participants included 230 Finnish (M = 29; SD = 3 months) and 283 Portuguese M = 30, SD = 4 months) toddlers and their teachers (n = 43 Finland; n = 29 Portugal). The children's behavioural self-regulation (attention, working memory, and inhibition control) was individually tested, and the teachers evaluated the children's self-regulation skills in the classroom. The quality of the teacher-child interactions (i.e., emotional and behavioural support and engaged support for learning) was evaluated using the CLASS-Toddler observation instrument. The analyses were conducted with path models using a complex option. The results for Finland show that the engaged support for learning was positively associated with children's attention and inhibitory control, and emotional and behavioural support was positively associated with children's inhibitory control. For Portugal, engaged support for learning was positively associated with children's attention. The results aid in recognizing the characteristics of teacher support that is beneficial to the development of children's self-regulation skills in two sociocultural contexts, hence being of relevance for teacher in- and pre-service training.