The COVID-19 context has created the most severe disruption to education systems in recent history. Its impact on child development was estimated comparing two cohorts of 4- to 6-year-old Uruguayan children: control (n = 34,355, 48.87% girls) and COVID cohort (n = 30,158, 48.95% girls) assessed between 2018 and 2020 in three waves, by a routinely administered school readiness instrument in public preschools. Ethnicity information is not available. For the COVID cohort, losses were observed in Motor and Cognitive development, Attitudes towards learning, and Internalizing behavior (range 0.13-0.27 SD). Losses were less pronounced among children from higher socioeconomic schools. These results extend the literature on the consequences of the pandemic on learning and early child development.