Child-internal and child-external factors predicting early and later vocabulary size in L1 and L2: A longitudinal study

Vocabulary size of bilingual children is influenced by both child-internal (child’s age, lexical and phonological processing skills, working memory, analytical reasoning) and child-external factors (quantity and quality of input, child’s language use, SES) (Hurtado et al., 2014; Paradis, 2011; Pham & Tipton, 2018, Sun et al., 2017). However, no study to date has explored the longitudinal impact of a large number of internal and external factors on the bilingual children’s vocabulary size. In this talk, we will summarise the results of a longitudinal study on Polish-English bilingual children living in the UK and Ireland. Children’s expressive vocabulary size was measured at the age of 24-36 months with the use of Polish and English CDI (Timepoint 1), and their receptive and expressive vocabulary size was measured at the age of 5;6-7;6 with the Polish and English Crosslinguistic Lexical Tasks (Haman, Łuniewska, Pomiechowska, 2015) (Timepoint 2). Background information about children’s language environment was collected through parental reports and at T2 also through in-depth semi-structured interviews. The data on children’s lexical and phonological processing skills, verbal and non-verbal working memory, and analytical reasoning skills was collected with the use of cognitive experimental tasks. The results show that children’s expressive vocabulary in Polish at T1 was predicted by child’s age, and in English by child’s language use. At T2, children’s receptive and expressive vocabulary in Polish was predicted by children’s phonological processing skills and their language use. Children’s receptive vocabulary in English was predicted by their phonological processing skills, while children’s English expressive vocabulary size was predicted by their phonological and lexical processing skills. We discuss how the role of internal and external factors in predicting vocabulary size changes over time and how the specific features of the Polish-English children’s language environment might explain this phenomenon.