This study explores sex differences in language and socio-emotional skills on children 7 months to 6 years old in Latin-America. Females had a significant advantage in both dimensions. To our knowledge, this is the first study to document sex differences in these dimensions at a very young age. In part, we believe this is due to our uniquely large sample size. We found geographical and cultural variation across the countries under study did not affect the gap. Within countries, variation in family characteristics, parenting practices and health investments did not explain the gap. The identification of biological and environmental factors is necessary to inform whether policy should tailor inputs to ensure equality of opportunities.