The relationship between first and second language in early vocabulary acquisition in bilingual children is still debated in the literature. This study compared the expressive vocabulary of 39 equivalently low-SES two-year-old bilingual children from immigrant families with different heritage languages (Romanian vs. Nigerian English) and the same majority language (Italian). Vocabulary size, vocabulary composition and translation equivalents (TEs) were assessed using the Italian/L1 versions of the CDI. Higher vocabulary in Italian than in the heritage language emerged in both groups. Moreover, Romanian-Italian-speaking children produced higher proportions of TEs than Nigerian English-Italian-speaking children, suggesting that L1-L2 phonological similarity facilitates the acquisition of cross-linguistic synonyms.

The current longitudinal study investigated the role of home language and outside home exposure in the development of Dutch and Frisian vocabulary by young bilinguals. Frisian is a minority language spoken in the north of the Netherlands. In three successive test rounds, 91 preschoolers were tested in receptive and productive vocabulary in both languages. Results showed a home language effect for Frisian receptive and productive vocabulary, and Dutch productive vocabulary, but not for Dutch receptive vocabulary. As for outside home exposure, an effect was found on the receptive vocabulary tests only. The results can be explained by the amount of L2-input that participants received. The Dutch input is higher for participants with Frisian as home language compared to the Frisian input for participants with Dutch as home language. The conclusions lead to further implications for language professionals working in language minority contexts.