This is the first of two articles that will examine the effect that the Old-Age, Survivors, and Disability Insurance (OASDI--Social Security) and the Supplemental Security Income (SSI) programs have in maintaining the income of poor and near poor families with children at a level that is at least equal to the poverty threshold. The articles also will evaluate the extent to which these programs augment the income of those families that receive benefits but who still remain below the poverty line, and look at the interaction between the OASDI and SSI programs and other income transfer programs, such as Aid to Families with Dependent Children (AFDC) and the Food Stamp program. The primary data source for this article is the second wave of the 1990 panel of the Survey of Income and Program Participation (SIPP). The principal findings are as follows: (1) During May 1990, OASDI and SSI benefit payments sustained the income of 1.1 million children above the poverty level; (2) these programs alleviated the effects of poverty for an additional 1.3 million children in families whose income remained below the poverty level; and (3) a significant proportion of those families that received OASDI and SSI benefits received additional assistance from other means-tested programs. This article looks only at survey data. The second article will consider survey data matched with SSA administrative records.