Complementary schools are an important research area of Second Language Acquisition study, involving issues of identity, linguistic socialization, second language acquisition, linguistic hegemony, etc. This article looks at the Czech Complementary School in Thessaloniki, whose main purpose is the transmission of the Czech language and culture to generations to come. At the same time, the article attempts to highlight the attitudes, identities and language management practices of mothers involved in Czech schooling and the process of language learning by their children. More specifically, the focus of the article is on mothers' language ideologies and management practices, i.e. on the intersection of research on complementary schooling and Family Language Policy. The role of mothers as custodians of the heritage language is highlighted. The research is based on ethnographic data: interviews, class observations and student reflection (via diary) on children's language use. The results show that these mothers are making efforts to transmit Czech to their children for reasons of culture, identity and 'good motherhood'.