Last time we went Osaka with my 6yrs old boy. He enjoy Universal Studio so much, and at 6yrs old.. quite a number of rides he can take. And those are not kiddy kiddy themepark ride.. are all with action movie theme. Such as we get on a boat tour... suddenly a shark raised from the water (JAWS) and the tour guide fire at the shark that causes fire explosion on the water. My boy love it so much thou being so young. Another is a building on fire old movie, we were like standing in the scene looking at burning fire and explosion, broken pieces flying around (but don't hit us the audience standing spot.. but gets very near enough to scare you), with grand finale that the stage we standing suddenly fall down half feet. This.. my boy grabbing my feet tightly but we all enjoy the stunt. But not sure bout your kids can take it. Of coz, they have kiddy stuff like sesame street.

If yours are boys, bring them to Namba toys area (forget the name) near Dotonburi. There sell plenty of Gundam very cheaaap...