This might surprise parents: A study of 1,000 low-income families in Chicago and two other big cities found that one in four kids between the ages of 11 and 16 said they'd already had sex.
Perhaps most shockingly, the average age at which low-income kids became sexually active was 12, according to the survey of families in Chicago, Boston and San Antonio reported online in the Children and Youth Services Review.
Nationally, experts have estimated that 13 percent of girls and 15 percent of boys have had sex by the time they're 16.
"Those people who say that kids don't have sex at that young of age should think again," said study co-author Brenda Lohman, an associate professor of human development and family studies at Iowa State University.
The research also found that children of more highly educated mothers and more involved fathers were less likely to have sex at a young age. Adolescents whose mothers had a technical degree or higher were half as likely to be sexually active compared to those whose mothers had a high school education or less.