They have go carts in Old Town Kisimmee, less than 3 miles from Pop Century, on I-192. The area looks a little shady, but its a nice walkthrough. We've never actually done the go-carts though.
Old Town as already mentioned and last time we were there they had this cool indoor glow in the dark mini golf. One night a week is car night (Fridays I think) http://www.old-town.com/
Recommend Fun Spot. Multi Level Tracks. They run "Rain or Shine" and it has the blacklight Mini Golf too. Wish they would put in a High Performance Indoor Track for the big kids in the Orlando area. They are a blast.