Yes two days is enough to do IOA and USF as long as you plan to arrive early and stay until close each day. Three days is ideal because you would have 1 day for each park, and then a day to redo some highlights (there are plenty of them!!) and catch anything you may have missed. Also remember to allow one night to check out CityWalk. There is something for all ages and in my opinion it rivals Disney's Pleasure Island. Have Fun!