The unconsolidated motor and cognitive skills that are typical of the early childhood period place infants, toddlers, and preschoolers at risk for a variety of traumatic injuries. Such injuries may include mild traumatic brain injury or concussion. Knowledge regarding the risk, diagnosis, outcomes, and management of early childhood concussion is limited, especially compared with what is known about concussion in school-age children, adolescents, and adults. This state-of-the-art review aims to provide current knowledge on the epidemiology, physical signs, behavior, and clinical outcomes associated with early childhood concussion. Research on this condition has been challenged by the need to adapt methods to the unique physical, behavioral, and developmental characteristics of young children. We provide information on observable symptoms associated with concussion, recommended approaches to care, and suggestions for overcoming barriers to research in this area. Developmentally appropriate efforts are needed to improve our ability to identify, evaluate, and treat early childhood concussion.