IOA has the Suess Landing which would be great for even the 9 month old-lots to look at kind of like Fantasyland. There's Camp Jurassic a playground type area that would be good too. Other than that not much at IOA
US has Barney show, Jimmy Neutron(use the stationary seats) Shrek 4-D(if your 4 yr old gets scared of the special effects have him take off the glasses movie will be a little blurry but nothing will seem like it flying out at him) DD3 liked Shrek.
Woody Woodpecker kid zone has a Curious George water playground which is awesome. Bring extra clothes or suit, they will get wet. Behind the water area is a really neat nerf ball type area, where they can shoot the balls down below or vacumn them up. Don't miss this area. It's was our kids favorite.
You may be able to do the ET ride. One word of caution: I took DD3 on this and she was fine with the effects, but you sit individually on bikes that move with a platform, some parts are up higher ala Peter Pan flight. Had my arm around her the whole time.
So guess my advice would be US