Past research shows that family language patterns (i.e., which languages are spoken in the family and by whom) are associated with bilingual children’s language use. However, it is unclear how input properties such as input quantity, parental proficiency, and language mixing may differ across family language patterns. It is also unclear whether the effects of family language patterns on children’s language proficiency remain when differences in input properties are controlled. We investigated (i) which family language patterns occurred in bilingual families in the Netherlands (n = 136), (ii) whether input properties differed across patterns, and (iii) how patterns related to children’s proficiency, once input properties were controlled. Home language situations were assessed through a questionnaire, children’s proficiency in Dutch and the minority language through vocabulary tests and parent ratings. Three language patterns were found: one-parent-one-language, both parents mixed languages or used the minority language. The results showed differences in input properties across all patterns, as well as effects of these patterns on children’s proficiency in Dutch and the minority language that disappeared once input properties were controlled. These findings do not provide robust evidence that family language patterns predict children’s proficiency, but rather, that input quantity is crucial.

Child characteristics, family factors, and preschool factors are all found to affect the rate of bilingual children's vocabulary development in heritage language (HL). However, what remains unknown is the relative importance of these three sets of factors in HL vocabulary growth. The current study explored the complex issue with 457 Singaporean preschool children who are speaking either Mandarin, Malay, or Tamil as their HL. A series of internal factors (e.g., non-verbal intelligence) and external factors (e.g., maternal educational level) were used to predict children's HL vocabulary growth over a year at preschool with linear mixed effects models.

The results demonstrated that external factors (i.e., family and preschool factors) are relatively more important than child characteristics in enhancing bilingual children's HL vocabulary growth. Specifically, children's language input quantity (i.e., home language dominance), input quality (e.g., number of books in HL), and HL input quantity at school (i.e., the time between two waves of tests at preschool) predict the participants’ HL vocabulary growth, with initial vocabulary controlled. The relative importance of external factors in bilingual children's HL vocabulary development is attributed to the general bilingual setting in Singapore, where HL is taken as a subject to learn at preschool and children have fairly limited exposure to HL in general. The limited amount of input might not suffice to trigger the full expression of internal resources. Our findings suggest the crucial roles that caregivers and preschools play in early HL education, and the necessity of more parental involvement in early HL learning in particular.