Expressive vocabulary development in children from bilingual and monolingual homes: A longitudinal study from two to four years

•The language trajectories of Spanish-English bilingual children differ depending on whether or not they have a native English-speaking parent.•Children with two native Spanish-speaking parents have better bilingual skills at 48 months than children with one native Spanish-speaking parent.•Children with two native Spanish-speaking parents have smaller English expressive vocabularies at 48 months than monolingual children.•Use of English in the home is a positive predictor of English vocabulary at 48 months only for children with a native English-speaking parent. The early course of language development among children from bilingual homes varies in ways that are not well described and as a result of influences that are not well understood. Here, we describe trajectories of relative change in expressive vocabulary from 22 to 48 months and vocabulary achievement at 48 months in two groups of children from bilingual homes (children with one and children with two native Spanish-speaking parents [ns=15 and 11]) and in an SES-equivalent group of children from monolingual English homes (n=31). The two groups from bilingual homes differed in their mean levels of English and Spanish skills, in their developmental trajectories during this period, and in the relation between language use at home and their vocabulary development. Children with two native Spanish-speaking parents showed steepest gains in total vocabulary and were more nearly balanced bilinguals at 48 months. Children with one native Spanish- and one native English-speaking parent showed trajectories of relative decline in Spanish vocabulary. At 48 months, mean levels of English skill among the bilingual children were comparable to monolingual norms, but children with two native Spanish-speaking parents had lower English scores than the SES-equivalent monolingual group. Use of English at home was a significant positive predictor of English vocabulary scores only among children with a native English-speaking parent. These findings argue that efforts to optimize school readiness among children from immigrant families should facilitate their access to native speakers of the community language, and efforts to support heritage language maintenance should include encouraging heritage language use by native speakers in the home.