Families in America are currently categorized into threes types according to their structure:
Nuclear family 
Single-parent
Extended family
Nuclear family 
The nuclear family is considered the "traditional" family. The nuclear family consists of a mother, father, and the children. The two-parent nuclear family has become less prevalent, and alternative family forms have become more common. These include homosexual relationships, single-parent households, and adopting individuals. The nuclear family is also choosing to have fewer children then in the past. The percentage of married-couple households with children under 18 has declined to 23.5% of all households in 2000 from 25.6% in 1990, and from 45% in 1960 
Single-parent
A single-parent (also termed lone parent or sole parent) is a parent who cares for one or more children without the assistance of the other biological parent. Single-parent homes are increasing more and more as married couples divorce, or as unexpected pre-marital pregnancies occur. The percentage of single-parent households has doubled in the last three decades, but that percentage tripled between 1900 and 1950. The sense of marriage as a "permanent" institution has been weakened, allowing individuals to consider leaving marriages more readily then they may have in the past.
Extended family
The extended family consists of grandparents, aunts, uncles, and cousins. In some circumstances, the extended family comes to live either with or in place of a member of the nuclear family. An example includes elderly parents who move in with their children due to old age. This places large demands on the caregivers, particularly the female relatives who choose to perform these duties for their extended family.