J.K.
The Magic House is tops. Membership is cheap if you get the one that's only for the school year. I guess technically that's a museum? but it is really a gigantic place to play!
Science Center is fun to run around in but that's a museum.
We take our daughter to Crestwood Mall for running around, but she's smaller, so your 8-yr-old would be bored.
We also go to McDonald's. I hate the food but she eats it, and she loves the playground.