That's already been thought of.
We went to an indoor playground for the second time ever the other day. The first time was several years ago when a little friend had her birthday party at a Cosmic Adventures clear across town. The one we went to the other day was on a much smaller scale, it wasn't total chaos and close to the house.
Here are some pics of the frenetic activities there - on the catwalk:
Going up the down slide:
Ye olde Ball Pit...