An increasing proportion of children grow up multilingually. However, the monolingual school system is still largely based on the local language. This points to the relevance of successful second language acquisition. The present study focuses on the language usage of parents when interacting with their children, something that has previously gained only little attention. Based on a longitudinal sample of 431 preschool children (M = 42.5 months), we examined factors that predicted parental language usage and whether different forms of parental language usage were associated with differential second language acquisition in children. The results show that parental language usage was associated with parental German language proficiency and their level of education. However, no association was found for parental duration of residence in Switzerland, income, the child's sex, presence of an older sibling, and the child's attendance at an educational institution. The parental usage of German in addition to the mother tongue had no positive effect on the children's German language acquisition, even with good parental German language proficiency.
