We've been taking my sister since she was really young and we still seem to always have a good time, it's just the height restrictions on everything start to make you question whether it's a good idea to bring young ones. Even in Suess Landing on both Cat in the Hat and High in the Sky Trolley.
IOA is definitely the better park for kids. My younger sister loves Suess Landing, Camp Jurassic and the Fantastic 4 spinner in Marvel Superhero Island. The park actually has a lot for kids, but when you look at headliners, the kids are still cut out of pretty much everything, which is Universal's biggest weak-spot.
Disney has a huge list of headliners that the entire family can ride with no height restrictions. Pirates, Haunted Mansion, Jungle Cruise, Fantasyland Dark rides (incl. IASW), The Great Movie Ride, Spaceship Earth, Kilimanjaro Safari's, Presumably the new Avatar Boat ride, etc.
Universal has none.