This study investigates social and ethnic differences in the use of early childhood education and care (ECEC) centers with different learning environments in an ECEC system with universal state-subsidized provision and low fees. Based on the German National Educational Panel Study—Kindergarten Cohort from 2011, we matched data on 587 groups in 253 ECEC centers with information on about 1,700 children and their parents and applied stepwise multivariate regression models. Research Findings: The results showed that social and ethnic differences tended to be small and were mostly not significant in terms of structural quality, activities, and materials in ECEC centers. In contrast, large disparities emerged regarding the use of ECEC centers with different compositions of children: Children of low educated parents and those with a non-German family language attended institutions with higher proportions of children from families with low educated parents and from families with a non-German family language, respectively. Practice or Policy: To counteract and compensate for the large disparities in the social and ethnic composition of children in ECEC centers, state funding rules and structural quality standards should take the composition more strongly into account.