Number of married husband and wife families that include "own" children under 18 years. Percentages are calculated out of the total number of family households with own children under 18 years.
According to the U.S. Census, "Family households" consist of a householder and one or more other people related to the householder by birth, marriage, or adoption. They do not include same-sex married couples even if the marriage was performed in an area issuing marriage certificates for same-sex couples. Same-sex couple households are included in the family households category if there is at least one additional person related to the householder by birth or adoption. Same-sex couple households with no relatives of the householder present are tabulated in nonfamily households. "Nonfamily households" consist of people living alone and households which do not have any members related to the householder.
U.S. Census Bureau, 2010 Census