Bilingual development has been linked to advantages in executive functions, but evidence from children with limited bilingual exposure remains scarce. This study examined the relationship between language development and executive functions in early bilingual second-language acquisition. Participants were 122 Japanese-speaking children (67 bilingual, 55 monolingual) attending a Japanese-English bilingual kindergarten in Singapore. Both groups showed comparable Japanese development, indicating smooth first-language growth among bilinguals. The findings further suggest that second-language learning can support first-language development. In cognitive tasks, bilingual children showed greater age-related improvement in reaction time on the Simon task, indicating better monitoring, which was linked to English proficiency and kindergarten experience. These results suggest that even limited second-language exposure in early childhood may relate to executive functions and first-language development, highlighting the need to study how bilingual experience shapes language–cognition links.