In this systematic review, we investigated how content knowledge (CK) and pedagogical content knowledge (PCK) in the domains of mathematics, science and literacy are represented in current research regarding early childhood pre- and in-service teachers. In our systematic literature search, we found 151 publications, of which 42 remained in the review after a close screening of the abstracts. We found that mathematics is the most represented domain in research in this field and that there is a focus on CK and PCK. Furthermore, we found a focus on in-service teachers rather than pre-service teachers and that qualitative as well as cross-sectional research methods are most common. The results indicate a need for research that links the different fields of knowledge as well as research in teacher education. Resulting questions and limitations of this study are discussed.