Early childhood development is a global priority, yet questions remain about how best to support disadvantaged children in low- and middle-income countries. We study the impacts of high-quality, center-based early childhood education on low-income children in Colombia through a randomized controlled trial, tracking participants longitudinally over five years. The program has sustained, positive effects on children’s health--including a 22% reduction in stunting--and positive effects on their cognitive development, partly driven by improvements in children's health and nutrition. These effects operate through the educational and nutritional components of the program, rather than through parental behavioral responses to the intervention. The cognitive gains do not persist in the last year of the study, as children from the control group progress earlier to primary school and catch-up, highlighting the importance of considering counterfactual care alternatives to understand the effects of preschool programs in low- and middle-income settings.