Here's a true story: When I was 13, I was inactive, overweight, and a poor student. My parents persuaded me to join my school cross-country team to get some exercise. The interactions and positive experiences I had while running changed my life. I had more energy, I was happier, and I started doing better in school (eventually, I even made it to the Olympics!).

Here's how to safely get children of all ages excited about running—for life.

AGES 6 AND UNDER

HOW FAR? Not very. At this age, playing chase or racing Dad to the mailbox is a great way to introduce kids to running.

RUN/WALK RATIO Run segments should be no longer than 10 to 20 seconds. Walk one to two minutes between each.

AGES 7 TO 9

HOW FAR? Start with a quarter of a mile. Every week, add a minute or two until you both can complete a mile. If your kid is having a blast, keep adding time until you're up to 3.5 miles—at that point you can talk about run/walking a 5K together.

RUN/WALK RATIO Jog for 10 seconds and walk for 40 seconds. Each week, increase the run portion by five seconds and decrease the walk portion by five seconds until you're at a 30/30 ratio.

AGES 10 TO 12

HOW FAR? Begin with a half mile. Each week, run an additional quarter mile. Build up to whatever mileage feels comfortable—most kids this age can run up to a 10-K.

RUN/WALK RATIO Start with one minute running/one minute walking. If that seems too easy, raise it to 2:1—work up to 4:1 if she continues to feel comfortable.