By Bureau of Labor Statistics
Government economists study data from the Current Population Survey and find that married persons volunteered at a higher rate (32.3%) than those who had never married (20.3%) and those with other marital statuses (21.3%). Furthermore, parents with children under 18 were substantially more likely to volunteer with a probability of 34.4% than were parents without children under 18, who had a probability of 23.6%.
Volunteering in the United States, 2006. United States Department of Labor: Washington, D.C.