This report presents findings on children's living arrangements as taken from the Survey of Income and Program Participation (SIPP). The SIPP is unique in that it records how each person is related to everyone else in the household. Detailed information on parent-child relationships is provided, allowing identification of biological, step, foster, and adoptive ties. Similar data are collected for siblings. With this additional information, it is possible to examine family structure in more detail than was possible in previous Bureau of the Census reports. The statistics contained herein are based on national-level estimates of children under 18 and their living situations, for the period June through September, 1991. The report's findings pertain to all children, regardless of their marital or parental status. Included in these findings was the fact that 73 percent of children under age 18 lived with two parents, 24 percent lived with one parent, and 3 percent lived with neither parent. Black children were 2.5 times more likely to live in a one-parent family than were White children. The report examines both traditional nuclear families and nontraditional families, and includes data on children in blended families, adopted children, extended families, and other arrangements. Five figures and 12 tables summarize the data. Appendixes include an overview of the SIPP program, definitions and explanations of terms, and source and accuracy of estimates. (RJM)