New Zealand has a growing population of Mandarin and Cantonese speakers, including children with speech, language, and communication disorders. However, the absence of language development profiles poses challenges in effectively identifying and addressing these concerns. This study aimed to capture the current state of monolingual, bilingual, and multilingual Mandarin- and Cantonese-speaking children living in New Zealand. Over 200 mothers in the Growing Up in New Zealand longitudinal cohort study identified their children as understanding Mandarin and/or Cantonese. Mothers completed newly adapted vocabulary and grammar checklists for New Zealand Mandarin and Cantonese speakers at the Age 2 data wave. Both of the adapted New Zealand Mandarin and Cantonese versions showed high reliabilities and validities. Unique demographic predictors of children’s vocabulary and grammar were mothers’ education, household deprivation level, and children’s birth order. Language status and maternal concerns were also unique predictors of children’s vocabulary development in Mandarin and Cantonese, with monolingual children whose mothers reported no concerns having higher Mandarin and Cantonese vocabularies. These results have rich implications for researchers, clinicians, and practitioners working with Mandarin- and Cantonese-speaking children in New Zealand and worldwide.