This case study focuses on an expert early childhood education and care teacher’s practical theory in language pedagogy when implementing bilingual pedagogy (Finnish–Swedish) in a linguistically heterogeneous group of children aged 3–5 years. Practical theory refers to teachers’ views of good teaching that guide their practices. Applying a mediated discourse analysis approach (nexus analysis), we examine the interplay of factors that promote and challenge changes in the practical theory of language pedagogy in early childhood education and care. The discourses show that the changes are related to Swedish use (a new language for the children) and the use of the children’s home languages. Several personal, interactional, and contextual factors circulate in the expert teacher’s discourses, affecting the changes in her practical theory. Personal factors include reflection, beliefs, and experiences. Feedback from parents and children represents interactional factors, whereas contextual factors cover concepts such as participation and language-enriched teaching. This study highlights the significance of the multiple interrelated factors that are present when an expert teacher’s practical theory of language pedagogy changes, which needs to be reflected upon both in the practice of early childhood education and in teacher training.