There is considerable policy interest in understanding the role of child care in children's development. Yet little research has examined whether individual children experience changes in child care quality across their early years, and less has included children's varying levels of exposure to care in analyses of child care trajectories. Using data from the NICHD Study of Early Child Care, this study seeks to fill these gaps by studying the non-maternal care experiences of children whose mothers work at some point during their early years. We find that few of these children experience continuously high-quality care or continuously low-quality care. Instead, many children experience changes in child care quality. Children from low socioeconomic status families are more likely to experience low-quality care than children who are never poor, but children who are never poor are more likely to have child care histories that include both low- and high-quality care arrangements. We discuss the implications of our findings for studies of selection into low-quality child care arrangements and the effects of child care quality on children's development. (Contains 9 tables and 2 figures.)