The study examined the effects of sociolinguistic background, nonverbal reasoning, and phonological working memory (WM) on heritage language (L1) and second language (L2) skills in Heritage Bilingual (HB) children attending preschool, considering relationships between L1 and L2 abilities. A total of 108 HB children completed vocabulary, morphosyntactic, nonverbal reasoning, and phonological WM tasks in both L1 and Italian (L2). Sociolinguistic background, including socio-economic status and linguistic history, was assessed through parental interviews. The analysis of reciprocal correlations between L1 and L2 showed within-language relationships and cross-language correlations only for morphosyntactic skills. Sociolinguistic background significantly influenced vocabulary skills, particularly in L1, while nonverbal reasoning impacted morphosyntactic skills, especially in L2. The findings highlight the importance of supporting families in enriching linguistic input in the heritage language and underscore the role of nonverbal reasoning and phonological WM in developing L2 competencies.
