Research findings: This study examined the dual language development and experience of the understudied Chinese dual language learners (DLLs). Twice in the preschool/pre-k year (about 4 months apart), we assessed 39 Chinese 3- and 4-year-old DLLs' receptive vocabularies in English and Chinese, interviewed 37 parents about the language use and richness of each language in the family context, and video-recorded activities in 10 classrooms to analyze teachers' and DLLs' language use (word types) in English and Chinese. DLLs' receptive vocabulary grew in both languages but only English, not Chinese, language use in the classroom increased across the year. Both in the family and early childhood contexts, Chinese DLLs experienced richer and increasing English exposure, while the Chinese exposure was impoverished and stagnant. Associations were found between both contexts and DLLs' dual language development. Practice or policy: These results highlight a central role of the family context in supporting the language development of DLLs and a significant and irreplaceable role of the early childhood teachers. Families and early childhood teachers need to be supported with more knowledge and resources to ensure the continued development of DLLs in both languages, and especially the home language, to help DLLs achieve bilingualism.