i am looking through my old universal guidebook, and here are all the rides that your kids should most likely be fine on:
universal studios:
A Day in the Park with Barney
Animal Actors on Location!
Back to the Future for children 7 and up (only if your kids are adventurous)
Beetlejuice's Graveyard Revue (the guidebook says for all, but i'd be cautious)
Earthquake (for children 5 and up)
E.T. Adventure
Fievel's Playland
Jimmy Neutron's Nicktoon Blast
Men in Black (the guidebook says 7 and up, but i know a timid 4 year old who went on it and was fine)
The Horror Make-up Show (I'd be cautious, because i've never seen it, and it is supposedly pretty frightening)
Jaws (7 and up, but not too scary)
Fear Factor Live
Woody Woodpecker's Nuthouse Coaster (4 and up)
at Islands of Adventure:
Spiderman (6 and up, but be cautious!)
Camp Jurassic
all Seuss Landing attractions
Jurrasic Park Discovery Center
Dr. Doom's Fearfall (6 and up, but it's like the tower of terror, so i don't advise it)
Dudley Do-Right's Ripsaw Falls (6 and up, but it's like splash mountain)
dueling dragons (6 and up, but i would NEVER let a child younger than 7 ride)
eighth voyage of sinbad (6 and up, but it's just a show, and there's not much too be frightened of)
Flying Unicorn (5 and up, but it's like woody Woodpecker)
If i ran the zoo
Me Ship, the Olive
Popeye and Bluto's Bilge-Rat Barges (4 and up)
Poseidon's Fury (6 and up)
Pteranodon Flyers (4 and up, the children you are riding with must be between 36 and 56 in. tall)
River Adventure (6 and up, it's a dinosaur version of splash mountain)
storm force accelatron (4 and up, like the mad hatter)
triceratops encounter
hope this helps!