Initiatives aimed at improving STEM education have largely focused on school-based programs, with the majority of STEM professional development targeting primary and secondary school educators. However, there is growing interest in STEM education in the early childhood years. This paper reviews the available evidence to explore the extent to which early childhood STEM professional learning programs are represented in the research literature. The review examines: 1. The emergence of research focused on STEM professional learning for early childhood educators; 2. The characteristics of these professional learning programs; and 3. The research evidence for the efficacy and impact of these programs. Using a scoping review methodology, our search yielded only 22 papers for analysis, with most of the studies published in the last seven years of the review period. Different views and definitions of STEM were evident across the studies, with few explicitly describing the integration of the four STEM disciplines. The majority of papers reported a workshops/in-service training approach. Unanimously, the 22 studies reported positive outcomes from the participants' engagement with early childhood STEM professional learning. However, the small number of research papers available for review confirms the need to build the evidence base for early childhood STEM professional learning.