Measurement of early childhood development at the population level has traditionally been neglected in Latin America. In this context, Uruguay stands out for having two population-based protocols: the Nutrition, Child Development and Health Survey (ENDIS), a home survey, and the School Readiness - Child Development Inventory (INDI). This paper aims to present both assessment experiences and analyse Uruguayan children's cognitive and socioemotional development according to sex and their families' socioeconomic status (SES). Comparisons were made between samples of children aged 1-6. Results suggest that girls generally show better development, except for internalized behaviour, but effect sizes tend to be small. In both surveys, children of high-SES show better development indicators than their low-SES counterparts, with larger effect sizes in fluid intelligence (problem-solving and mathematics). Differences between SES-quintiles consolidate after 30 months of age. Our findings contribute to the development of evidence-based public policies aimed to reduce developmental disparities.