This ongoing study addresses examines relations between concurrent, multiple child care arrangements, or arrangement multiplicity, and young children's health. Specifically, a longitudinal, comprehensive dataset is used to relate changes in the number of children's child care arrangements to changes in children's communicable diseases and general health from birth through age 5. The mediating effect of peer exposure and the moderating effects of child gender and family income will be tested. It is expected that increases in the number of child care arrangements will be associated with increases in the incidence of children's communicable diseases and decreases in children's general health, and this relationship will be stronger among boys and those living in lower-income families. The research questions are: (1) Is the experience of multiple, concurrent child care settings related to increases in the incidence of communicable diseases and general health among children from birth through age 5?; (2) Is the relationship between arrangement multiplicity and child health mediated by the total number of children to which the child is exposed?; and (3) Is the relationship between arrangement multiplicity and child health stronger among boys and children from low-income families than among girls and children from higher-income families?