Whether you're logging mega-miles to get ready for the Broad Street Run on May 6 or are just hoping to save time and have a bonding experience by dragging your kids along on your next power walk, here's news: Kids simply can't work out the way adults do.  I learned this the hard way several years ago, when I tried to get my then 5-year-old to fitness-walk with me on a beautiful walking trail near work.

We'd walk a little … then stop to look at a flower. Walk a few more steps … then stop to goof off on the exercise equipment that dotted the trail. Walk a bit more … then stop for a sip of water. After about 5 minutes I realized that it just wasn't working. I was frustrated. Then I interviewed kids' fitness expert Melinda Sothern, Ph.D., of a Louisiana State University, for an article about walking with kids and I understood.

Sothern, author of Trim Kids: The Proven 12-Week Plan That Has Helped Thousands of Children Achieve a Healthier Weight, told me that before they become teenagers, kids simply aren't ready to handle the kind of hard-charging, lengthy work-outsadults prefer. Their bodies and minds aren't equipped for it. It was an ah-ha moment.

After that I stopped dragging my kid along on fitness walks, but made time for fun walks – like the year we strolled up and down our street during Christmas vacation, singing the 12 Days of Christmas and hopping on and off rocks as we went.

Here are three activity mistakes parents make – and fixes that'll keep your kid moving:

Mistake: You're looking for a serious work-out.

Fix: Make physical activity fun.

Walking two miles in 24 minutes or trying to maintain a target heart rate may satisfy your fitness goals, but the measures adults focus on during exercise  — time, distance, and intensity — mean sheer drudgery for most kids. "There's not a single exercise scientist in the world who would recommend an adult, structured program for kids and most teens," Sothern told me. "It has to be fun."

Mistake: You want to move at a steady pace

Fix: Change it up.

Before they hit age 14 or 15, a kid's natural activity pace is variable – with short bursts of intense activity and plenty of downtime. "Children are not like adults when it comes to exercise," Sothern said. "They have immature metabolic systems. They don't have the same hormones as adults. They can't sustain high-intensity brisk walking for long periods of time, and steady-state exercise doesn't get them into "the zone" the way it does for grown-ups. Parents need to be aware of that."

Mistake: You're not deploying an important fitness "tool" – their friends.

Fix: Invite another kid along.

Kids don't want a work-out partner or a coach — they'd rather share the fun. You can do that, but don't overlook a secret activity weapon: Other kids. Invite a friend along to the park or for a stroll on a local walking trail. Younger kids want someone who will run, skip, pick flowers and giggle with. Teens may be more into it if they can walk with a friend, while you tag behind or walk ahead. A happier kid, Sothern says, is more likely to get excited the next time you say "want to go for a walk"?