The MacArthur-Bates Communicative Development Inventory (short form) was adapted for Samoan and Tongan speakers in New Zealand. The adaptation process drew upon language samples from Samoan and Tongan parent-child dyads with 20- and 26-month-old children and adult informants. The resulting 100-word language inventories in Samoan and Tongan, plus a single question about word combinations, were then administered to over 600 mothers of 2-year-olds in the "Growing Up in New Zealand" pre-birth longitudinal cohort study who identified their children as understanding Samoan or Tongan. Most mothers were able to complete the inventories without the help of an interpreter or interviewer. Important demographic correlates of children's vocabulary and grammar were mothers' country of birth, education, and deprivation level, and children's birth order. Mothers' birthplace was the single best predictor of children's vocabulary development in Samoan and Tongan, with children of mothers who were born outside New Zealand having higher Samoan and Tongan vocabularies. Clinical implications are discussed, along with future analyses of the language development of these children from the Growing Up cohort.