Many children miss opportunities to be active, says a report in the American Journal of Preventive Medicine. One in three U.S. children live within a mile of school, but barely half of those regularly walk or bike to their destination. Among the least likely to take the active path to class? Children who live in the South or rural areas or have college-educated parents. Of the more than 7,000 children ages 9 to 15 studied, children between ages 11 and 13 were more likely to walk or bike to school than 9-year-olds.