R.J.
When my son was little (and not so little), I'd just play with him on the equipment. Oftentimes, we'd end up with a whole swarm of kids playing as well; Tag, hide and seek, many many many "monster" games (don't touch the lava!, pirates are coming!, pretend to be a bear! no, a seal! no, a _____), cartwheel races, handstand competitions, blind man's bluff. Then we'd kick the soccerball around, play basketball... and by the end, I'd be absolutely pooped... but I'd have run, climbed, jumped, swung for faaaaar longer / doing soooo much more than standard exercise routines. Actually keeping UP with a whole swarm of kids is a REAL challenge!
As he's gotten older... he comes along with me on long walks (he rides his razor or skateboard or bike because it's more fun for him than walking 6mi, he used to like running them, but he prefers rolling, these days)... and due to a dirth of childcare at the beginning, and because it's just plain fun later... I looked for sports we could do TOGETHER. Instead of me sitting and watching. Swimming and Snowboarding and Basketball. I can't keep up with him anymore, and he's starting to get to the age where soon he'll be peeling off with friends (turning 10 this year)... but I'm still out and doing!