Gender differences in early childhood development are under-researched in low- and middle-income countries (LMICs) where almost 90% of the world's young children live. This study examines the direction, magnitude, and variation of gender similarities and differences in 3- and 4-year-olds' early childhood development in 71 low- and middle-income countries (LMICs). Moreover, we explore whether country-level gender inequality correlates with gender differences in early development. We analyzed Early Childhood Development Index (ECDI) data from UNICEF's Multiple Indicators Cluster Surveys and the Demographic and Health Surveys between 2010 and 2019 (n = 226,980). Using logistic regression, we estimated children's odds of being developmentally on track in literacy-numeracy, approaches to learning, social-emotional, and physical domains. We also used meta-analytic regression to examine associations between early childhood development and country-level indicators of gender inequality. In approximately one-half of LMICs, odds of being developmentally on track did not significantly differ for girls and boys; in countries with significant differences, girls were more likely to be on track than boys (odds ratio [OR] = 1.21, 95% confidence interval [CI] = [1.18-1.24], p < 0.001). Differences favoring girls were largest in the social-emotional domain (OR = 1.27, 95% CI = [1.24-1.30], p < 0.001). Country-level gender development index explained a substantial amount of variation in gender differences across countries. Overall, findings suggest that when gender differences exist, girls are more likely than boys to be developmentally on track, particularly in the social-emotional domain and in countries with greater gender equality.