To mix or not to mix? The relation between parental language mixing and bilingual language development.

Multilingualism is becoming increasingly common across the globe, resulting in many children being raised with more than one language. It is natural for multilingual children to be exposed to language mixing (Kremin et al., 2022), the phenomenon where two languages are being alternated within a conversation. Merely a handful of studies have investigated the relation between language mixing in children’s language input and children’s development in their different languages, and results are equivocal. Byers-Heinlein (2013) found that a higher frequency of parental language mixing might be negatively related to children’s early vocabulary development. However, only one following study was able to replicate the negative relation (Carbajal & Peperkamp, 2020). Other studies have found either null-effects (Place & Hoff, 2016) or even a positive relation: children who heard more language mixing within-sentences had larger vocabularies (Bail et al., 2015). One possible explanation for these differing results is that studies have measured language mixing via various methods. The current study will investigate the relation between the frequency of parental language mixing and bilingual children’s (receptive and expressive) vocabulary and grammar outcomes in two different bilingual communities in the Netherlands (Turkish-Dutch and Polish-Dutch). Furthermore, we will investigate whether switches within a sentence (intra-sentential; Poplack, 1980) have different relations to the various language outcomes than switches between sentences (inter-sentential) and whether the method of measuring language mixing influences the found relations.