This report examines the care arrangements of children under age 13 who are in families with annual incomes below $15,000 using nationally representative data from the National Child Care Survey 1990 and its low-income-data supplement. Although many low-income children are cared for exclusively by their parents, supplementary care arrangements play an important part in the lives of the majority of low-income children. For many families, child care consists of a combination of arrangements, and many children use more than one type each week. One of the most important findings is that care arrangements used by children with employed mothers are quite similar to those used by unemployed mothers enrolled in education or training programs. Child care financially burdens many families, and low-income families spend a substantially greater share of their income on the care of their children. Families in poverty spend an even higher proportion of their family budget on child care than other low-income families. Nevertheless, the majority of low-income families report that they do not receive any financial assistance with their supplemental arrangements. Four appendixes provide information about the study methodology and a glossary. Eleven tables, 36 figures. (Contains 5 references.) (Author/SLD)