Check out CityWalk. They have live street performers on the streets sometimes. Also, on the stage in the Plaza or up the flight of steps behind that stage, on the street, in front of Pat O'Brien's they will often have some hosts doing particpatory games and such to rev the crowds up. Your child might find some of this fun to watch (although it seems to be aimed at older teens and younger 20-somethings).
Some CityWalk shops might be entertaining. Captain Crackers has wacky wind up toys and the like and a place to try them out. (Hang on to your wallet!) Acroos the way is a shop called Glow that has some neat blacklight stuff that your child might find interesting.
Otherwise, you might want to hop in the car and head for FUN SPOT. It's off International Drive, just on the other side of I-4 from Universal. If you head south on Kirkman Road, look for the large ferris wheel on your left. Then turn left on I-Drive and left again at the next street.