More rigorous research is needed to build the evidence base on the impact that lower child-to-caregiver ratios have on children’s development, health, and safety in early care and education settings, particularly in the infant and toddler years. The few causal studies identified for this review suggest mixed impacts, but the observational research conducted up to this point is promising, and it suggests that lower ratios and smaller group sizes may lead to more positive caregiving, better cognitive outcomes, and fewer illnesses among children. (author abstract)