The current study examined whether the vocabulary skills of sequential bilingual children who learned Cantonese as a home language (L1) and English as a second language (L2) were predicted by the amount of L1 and L2 used at home. Ninety-two preschool children who learned Cantonese as L1 were recruited from a Head Start program. The amounts of L1 and L2 used at home were measured using parent questionnaires. Mixed patterns of L1 and L2 use were found across family members and home activities. After controlling for time spent in preschool, regression analyses showed that the amount of L1 and L2 used by individual family members, with the exception of older siblings, was not significantly linked to children's vocabulary skills. In contrast, the language used during some home activities such as dinner and book reading significantly predicted children's vocabulary knowledge. Implications for family involvement in facilitating children's vocabulary development are discussed.

Purpose This research project examined the vocabulary growth patterns of typically developing (TD) Cantonese–English dual language learners (DLLs) and their peers who are at risk for language impairment. Method Two studies were done. Study 1 examined the concurrent validity of a pilot vocabulary screening measure, the Kai Ming Vocabulary Test, that was designed for Cantonese–English preschool DLLs. Participants were 53 preschool children who learned Cantonese as their first language (L1) and English as a second language (L2). Their scores on the Kai Ming Vocabulary Test were examined in relation to their language sample measures, including number of different words and mean length of utterance, in L1 and in L2. Study 2 examined the vocabulary growth patterns of 24 TD Cantonese–English DLL preschoolers and 24 DLLs who are at risk for language impairment (At-Risk group). Each child was tested 3 times during an academic year. Results Results of Study 1 showed that children's vocabulary scores ( n = 53) were significantly correlated with their language sample measures in each language. In Study 2, hierarchical linear models were used to compare the TD and At-Risk groups. Results showed that children in the At-Risk group had lower L1 receptive vocabulary scores and children in the TD group had relatively higher L2 expressive vocabulary gains. Conclusions Children who are at risk are likely to continue to have lower vocabulary knowledge compared to their TD peers. The growth trajectories of DLLs provide valuable information for early identification and intervention.