This study explored whether the directionality of the relation between majority language and various facets of socioemotional development (three to 5 years old) differs between children with different language backgrounds. 12,951 children (49% girls; 85% White, 6% Pakistani and Bangladeshi, 3% Black, 3% Mix, 2% Indian) from the British Millennium Cohort Study (2001–2006) were included in two-time-point cross-lagged analyses. Models controlling for important covariates found a bidirectional association for monolinguals (βs = .05, −.07, −.04), a unidirectional effect of majority language on socioemotional difficulties for dual language learners (DLLs) speaking English and minority language(s) at home (β = .14), and a unidirectional effect of socioemotional strength on majority language for DLLs speaking only minority language(s) at home (β = −.17).