National estimates of the numbers of families with step, adopted, and biological children have not previously been developed. In this work, parent types for children in married-couple families were indirectly identified by using marriage and birth dates. Families were then classified by the types of children present. A large majority (79 percent) had only biological children; however, a significant minority (16 percent) had at least one stepchild and 4 percent had at least one adopted child. This analysis provides national estimates of the numbers and characteristics of married-couple families with step, adopted, and biological children.