It's never too early to start running. Many kids get their first taste of it from the seat of a running stroller.

"As long as it's a fun activity, children can start running at any age," says pediatrician Terry Adirim, who is board certified in sports medicine. She advises starting them off with short noncompetitive races or even walking. The American Running Association's Web site (www.americanrunning.org) outlines a 12-week walking program that encourages family fitness.

All athletes run the risk of injuries; runners are no exception. Kids tend to be more resilient than adults and heal faster, Adirim says. Common problems include heel pain, twisted ankles and stress fractures. Proper-fitting shoes and stretching can help cut down on injuries. Adirim also stresses the importance of good nutrition, staying hydrated and, for girls, getting enough calcium. Parents should be aware that girls who take up running sometimes have irregular menstrual cycles.

Not all marathons allow younger teenagers to participate; the Marine Corps Marathon does. "Training for a marathon is a lot of wear and tear on the body," Adirim says. "It's not necessary for teenagers to run marathons. But if they insist and it's okay with the parents, it is important that their diet be carefully monitored to make sure they're getting enough calories, that they're not suffering from overtraining syndrome and that it doesn't interfere with their schoolwork."

"In general," she adds, "there are many more reasons to take up running than not to. It's a great activity for the whole family."

-- Janice L. Kaplan