BACKGROUND The United Nations (UN) created the Multiple Indicator Cluster Surveys (MICS) to monitor progress toward achieving goals of the World Declaration on the Survival, Protection, and Development of Children and its plan of action. The MICS is nationally representative and internationally comparable. METHODS In this study, we use MICS data from 51 low- and middle-income countries on 159 959 children between 36 and 59 months of age. To index national development, we used the 2013 UN Human Development Index (HDI), which provides data on country-level life expectancy, education, and income. To index child development, we used the Early Childhood Development Index (ECDI), which assesses literacy and numeracy, socioemotional development, physical health, and approaches to learning. RESULTS Children’s literacy and numeracy, socioemotional development, and approaches to learning all increase linearly as national development on the HDI (especially education) increases. Overall, the HDI revealed a positive association (r = 0.40) with the ECDI: the HDI explained 16% of variance in children’s ECDI scores and was the most influential predictor of ECDI scores examined. HDI-ECDI relations are robust, even when we control for multiple demographic aspects of children (age, sex), mothers (age, education), and households (size variables) as covariates. No family demographic variable was a stronger predictor of child development than national development. CONCLUSIONS To promote child development, low- and middle-income countries need to develop and implement policies that ensure national health and wealth and, particularly, the educational achievements of children’s caregivers. These findings are faithful to the World Summit for Children and inform the UN Sustainable Development Goals, which drive the international development agenda through 2030.