Parents, teachers and institutions often attempt to implement monolingual policies in bilingual settings, believing that they thereby facilitate children's bilingual development. Children, however, often have their own communicative agendas. In this study, we investigate how the twofold language policy of an English-medium preschool in Sweden is put into practice in everyday interaction. The results show that children (aged 3-4) develop a broader range of code alternation practices than the staff uses in their interaction with the children. The paper analyses several examples of spontaneous interaction either between staff and children, or among children playing with each other in the preschool. We show how the preschool's English language profile in practice becomes a bilingual policy, which encourages children not only to acquire English and Swedish in the preschool, but also to learn different ways to manage their bilingualism in the school context.