On a daily, weekly, or yearly basis, young children transition among a range of care environments including parental care, formal center- and home-based child care, and informal arrangements with relatives, neighbors, and babysitters. Most previous child care research has examined child development in relation to a single type of care or children?s cumulative care experiences while little is known about the impacts of child care multiplicity or normative changes in care over time. The current project examines the early child care patterns among children in the National Institute of Child Health and Human Development?s Study of Early Child Care and Youth Development (N = 1,364). Associations between the number, type, and combinations of child care arrangements, both at one point in time and over their first five years of life, and children?s social-emotional and behavioral outcomes are investigated in three studies. In Study 1, the child and familial factors associated with the use of concurrent, multiple, nonparental child care arrangements are explored, finding that child age, primary child care type, family structure, and maternal employment characteristics predicted the use of multiple arrangements. Study 2 employed within-child fixed effects models to examine associations between changes in the number of concurrent child care arrangements and changes in mother- and caregiver-reported behavioral outcomes among children during the preschool period. Between 11 and 13 percent of children were in two or more concurrent child care arrangements at 2 and 3 years of age. Increases in the number of arrangements were related to increases children?s concurrent behavior problems and decreases in prosocial behaviors. Finally, Study 3 examined relations between the developmental timing of child care type and peer exposure and social-emotional and cognitive outcomes at school entry. Results indicate that cumulative center care experiences predicted cognitive competence but more behavior problems. Continuous home-based care was associated with higher social status at school entry through smaller peer groups during the preschool period. Together, findings suggest that child care research should adopt more nuanced approaches to examine children?s care experiences in relation to their subsequent development. Policy implications include enhancing the supply of full-time, high-quality early care and education across the first five years to jointly support children?s developmental needs and parents? employment demands. Future research should examine the mediating pathways between child care patterns and children?s development, as well as macro-level supply and demand considerations.