Preparing teachers for early language education is crucial for the quality of ECEC education. In the recent decades, the role of teachers and consequently, the education of teachers, has been a major, increasing concern both politically and in research. Worldwide, there are huge variations in how to prepare teachers for the complexity of language education for children in early childhood education contexts, in relation to language, literacy and multilingualism.    The paper presents previous research on ECEC teacher education research, in particular studies related to development of the knowledge base for preservice and in-service teachers, and discusses some common challenges for ECEC teacher education.   The traditional theoretical underpinnings for language knowledge base in ECEC teacher education concerns the subject knowledge that language teachers need for their teaching practices. This tradition is recently challenged by more critical and sociocultural perspectives, suggesting that language teacher education should be based more on language as a social practice and involve more critical approaches on how language, power and identity are relevant for language teaching. The empirical studies related to teachers’ language knowledge base have mainly revolved around in-service teachers’ practical knowledge and beliefs about language development, literacy and second language/multilingual teaching, documenting the importance of teachers’ experiences. The amount of studies that are oriented towards professional development is increasing. There is consensus that in-service teacher education has an impact on classroom practices and consequently on children’s language development, and that the effort must be extensive to make a difference. The requirements for the teachers’ knowledge base appear vague and unarticulated. The younger the language learners, the lesser the requirements of this knowledge base. Grounded in discussions in the teacher education field, this presentation foregrounds more research at the educational level and scope, as well as the scientific and theoretical knowledge base of language in ECEC teacher education.