Getting little kids to exercise is easy. They naturally run around all the time...in the house, at school, in the yard. But the older kids are a tougher group. Although my pre-teen does have gym class twice a week....only when she decided to join cross country was she really getting a good amount of exercise (30mins/day (we should all do that!)). If you have the time and money, park district or YMCA programs are great. If you don't, you have to get make it a priority to make sure you are all getting exercise in the day. It is as important as homework and eating dinner together.
Here are some ideas...
Get some exercise or dance DVDs from the library. Encourage your kid to do them or offer to do them with your child. (My daughter got a yoga dvd/book for Christmas). There some good kids hip hop dvds.
Walk! In my neighborhood, my daughter can go on a walk around the block (or two) on her own. If that is not the case, walk with your child.
Bike! My daughter loves to ride her bike.
Jump! Go and buy a jump rope...your child can jump inside or out. Put on some music and jump for a few songs.
Have friends over for a dance or karaoke party!
See if there are sports teams or intramurals at your child's school....they are typically free and take place after school at school (so no driving around!). If not, get a couple parents to request or organize something.
I make my kids go outside for 30mins when the weather permits....the oldest makes obstacle courses and coaches her siblings in soccer and basketball. They also perform stunt shows.