Physical activity (PA) in the early years is foundational for growth and development and associated with numerous health benefits. However, the prevalence of PA participation among the pediatric population with disabilities is less clear. This systematic review aimed to synthesize the existing literature on PA levels of young children (0–5.99 years) with disabilities. Empirical quantitative studies were collected from seven databases and reference hand searching; 21 studies were included in the review. PA levels varied widely based on disability type and measurement strategies, but overall, PA levels were low. Future research should address the underrepresentation of measurement and reporting of the PA levels of young children with disabilities.