One in six children live with a half sibling under 18

By Brian Knop

WASHINGTON, D.C. – It’s not uncommon for children to live with siblings who share just one biological parent. In fact, one in six children under 18 live with a half sibling, according to U.S. Census Bureau estimates.

Of the 73.5 million children under age 18 in 2014, 17.0 percent (12.5 million children) were living with at least one half sibling also under 18.  

These estimates come from the redesigned Survey of Income and Program Participation (SIPP) 2014. The latest estimate is six percentage points higher than the percent of children living with a half sibling shown in the previous SIPP panel in 2009 (10.8 percent). 

There was a parallel six percentage point drop in the share of children living with only full siblings (those who share two biological parents): 57.5 percent in 2014 compared to 64.2 percent in 2009. 

Changes to the data collection process for these estimates explain these differences more so than an actual change in American families between 2009 and 2014.

Changes in SIPP Data Collection

Unlike previous panels, the 2014 SIPP includes an expanded fertility section that includes whether people have children with more than one person.

Sibling information now comes from answers to these new fertility and demographic questions. There were also changes to data processing that improved the accuracy of sibling estimates.

In previous panels, a respondent identified how each person is related to every single person in the household (e.g., parent, child, grandparent, cousin, nonrelative). 

Often, respondents may not think of sibling relationships in specific demographic terms. In their day-to-day lives, people define family relationships not just by technical terms, but also based on personal and shared histories. 

In previous SIPP panels, survey respondents may have misidentified half siblings in their household as biological full siblings even though they shared only one biological parent. This is more likely to happen when siblings are under age18 and share daily routines and developmental milestones.

The SIPP question changes reduced the survey length for many respondents and provided a more accurate estimate of half siblings.

Number and type of siblings

Estimates show that children live in a variety of sibling configurations — with varying numbers of biological, half, step or adopted siblings. Whether children live with siblings varies depending on whether they live with both parents or with their mother or father only:

  • More than 4 in 5 children (84.6 percent) living with two parents also live with at least one sibling. That’s higher than the percentage of children who live with at least one half sibling and their mom only and at least one sibling (74.4 percent); or with their dad only and at least one sibling (63.8 percent).
  • A higher percentage of children living with their dad only also live exclusively with full siblings — 48.3 percent compared to 39.0 percent living with their mom only.
  • The presence of at least one stepsibling is higher among children living with their dad only (6.1 percent) than among children living with either their mom only (0.9 percent) or with two parents (2.6 percent).

It’s more common for children living with their mom only to have at least one half sibling present (32.5%). Only 7.6% of children living with their dad only and 12.8% of children living with two parents have one half sibling – or more – living with them.

More children live with two parents than with a mother or a father only, regardless of the number of siblings under 18 in the home.

The least common sibling arrangement among children living with two parents — no siblings — is still more common than the most common sibling arrangement (one sibling) among children living with a mother only.

Similarly, more children live with a mother than with a father only, regardless of the number of siblings present.

There are more children living with a mother only and three or more siblings (the least common sibling arrangement among children living with a mother only), than any of the individual sibling arrangements among children living with a father only.

These estimates allow for a more detailed analysis of children’s living arrangements and how they are linked to child well-being.

Brian Knop is a family demographer in the Census Bureau’s Fertility and Family Statistics Branch.