Some one needs to make this a Important Question, it's asked almost everyday. You might check out so of the other threads because this is very common question.
Universal has a lot of kid rides and areas created for the youngsters at both parks.
USF: KidsZone is targeted just at kids inside KidZone you have Animal Planet live all kids love animals. E.T., Curious George Goes To Town, which is a water type playground. Fievel's Playland, another playground with a kid coaster and water slide. A Day In The Park With Barney, a kid show with the kids favorite purple dinosaur.
Outside Kidzone you have Nickelodeon Studios, where all kids go to get slimed and be on tv or on Slime Time Live. Men In Black is a sort of kiddy ride as is Back to the Future.
I guess you would have to use your best judgment for the rest of the rides.
IOA: Gets a rep as a Teenage park and I don't know why most of the park is more for little kids then Teenagers.
Suess Landing is a one big huge playground for kids with rides like, The Cat in the Hat, The Caro-sel-suess, 1 fish, 2 fish, blue fish, red fish and If I ran the zoo.
The lost continent has a kid coaster The Flying Unicorn.
Jurassic Park: This Island is a kid area, I am not too sure about the River Adventure that 85-Foot drop scares me but I force myself on it. You your best judgment on that ride as well, all kids love dinosaurs so they might like seeing them. Triceratops Encounter is where kids can see a life size Triceratops they can even pet it. Camp Jurassic is another kid playground. Pteranodon Flyers is an exclusive kid ride, if you are taller then 56 and don't have a kid guess what your not going on. The Discovery Center is another indoor kid interactive area where they can actually see a baby raptor hatch.
Toon Lagoon: Has kid shows with characters like Popeye, A kid interactive playground at Popeye's Ship. Then has 2 rides Ripsaw Falls I never have been on so can't say, Then Popeye and Bluto's Bilage-Rat Barges which any kid would love.
Mavel Super Hero Island: Spider-Man and The Storm Force Acceletron would be all I would recommend.
So there is plenty of things for little kids to enjoy, use your best judgment and you'll be ok.