Of these children, 42.7 million lived with both parents who were married to each other. Another 4.1 million lived with a biological mother and stepfather, according to Living Arrangements of Children: 2004 An additional 19.3 million children lived with one parent, with the majority of those (88 percent) residing with their mother.

There were 12.2 million children (representing 17 percent of all children) who lived with a stepparent, stepsibling and/or half sibling.

Among children in these "blended" families, 71 percent lived with at least a half sibling, 46 percent with a stepparent and 10 percent with a stepsibling.

Other highlights:

Overall, 94 percent of children lived with at least one biological parent, while

8 percent lived with at least one stepparent and 2 percent lived with at least one adoptive parent.

Editor's note: The report can be accessed at http://www.census.gov/prod/2008pubs/p70-114.pdf.

As for parents, 30.2 million men lived with at least one of their children younger than 18, compared with 37.8 million women. A higher percentage of the mothers (94 percent) lived with their biological children than the fathers (85 percent).

Most children lived with at least one sibling (79 percent). The majority (64 percent) lived with one or two siblings, while 5 percent lived with four or more siblings. Twelve percent of children younger than 18 lived with a half sibling.

Overall, 13.4 million children lived in extended families containing someone other than their parent or sibling. Of these, about 6.5 million lived with at least one grandparent, with 1.6 million of these children having no parent present.

Approximately 2.2 million children were living with a mother who married, divorced or was widowed in the year prior to the survey date.

Of the 18.7 million children living with their unmarried biological mothers, 18 percent had mothers who were living with unmarried partners. In comparison, of the 4.2 million children living with their unmarried biological fathers, 53 percent were living with fathers who were living with an unmarried partner. Overall, 5 percent of children younger than 18 lived with a cohabiting parent.

These data were collected from June 2004 through September 2004 in the Survey of Income and Program Participation. As in all surveys, these data are subject to sampling and nonsampling error. For further information on the source of the data and accuracy of the estimates, including standard errors and confidence intervals, go to http://www.sipp.census.gov/sipp/source.html.