So below is a comparison of Universal to Disney rides I did for another thread. This should get you started. I have the Universal attraction, and then the Disney equvilant beside it. I added notes on scariness to this where I could remember.
And you'll have to get someone to update you about Diagon Ally as that wasn't open yet my last trip.
IOA - Islands of Adventure
Seuss Landing:
Caro-Seuss-el - Prince Charming Carousel (with Seuss creatures to ride on)
The Cat in the Hat - Winnie the Pooh (plus some spinning) Less spinning than Teacups at Disney, but the same type of spinning. I think you can ask for a non-spinning ride vehicle.
One Fish, Two Fish, Red Fish, Blue Fish - Dumbo (if someone was shooting those fire hoses at you while you rode)
The High in the Sky Seuss Trolley Train Ride - People Mover (with a narrated story and more visually to look at) Could be scary if afraid of heights
If I Ran the Zoo - NA - interactive outdoor playground with splash sections
The Lost Continent:
Eighth Voyage of Sindbad Stunt Show - Indiana Jones Stunt Show
Mystic Fountain - similar to any of the "living" objects/places at Disney
Poseidon's Fury - NA - a dark tour through underground ruins that ends with a water / fire / light show – From your description this would be a big NO. You start off like you are on a tour of a dig site, and then the power goes out, and it is pitch black. It only goes downhill from there. The whole premise is that an evil god is after you because you’ve unleashed this curse, and that everybody is going to die or something like that. It’s corny and funny if you are old enough to realize it is all fake, but there were a number of hysterical children screaming in terror when I went. You’ve got loud noises, scary light effects, extremely dark rooms, an evil entity after you, a guide playing up the drama of this evil thing, and then to top it all off you have this huge battle at the end with a giant hologram of the evil guy.
Wizarding World of Harry Potter - Hogsmeade:
Frog Choir - Probably closest to Harmony Barber Shop minus instruments (just a short performance on a small stage of 4 people singing)
Flights of the Hippogriff - Barnstormer (very short kiddy coaster, a little tamer)
Dragon Challenge - NA - 2 intertwined inverted outdoor coasters that go upside down
Forbidden Journey - NA - closest to Spider-Man or Transformers if you rode in a Soarn'n type vehicle
This again I think would be a No. It is a very dark ride. Even if you sit right beside your child, you cannot see them or hold their hands. They will feel completely alone. There are lots of dementors, dragons, giant spiders, all attacking you. And to make it all worse your field of vision is very limited, so you cannot see if something is there until it pops up right beside you, and you can’t see your legs either which is what really creeps me out. You are flying over all these monsters and your legs are right by them, but you can’t see them! For me what you can’t see is scarier than what you can on this ride. You really feel like you are in the book or movie not a ride because you can’t see any ride aspects like walls or other vehicles.
Jurassic Park:
Camp Jurassic - Boneyard at AK (kids outdoor playground / climb area)
Jurassic Park River Adventure - Cross between Jungle Cruise and Dinosaurs (with a drop / splash at the end) Animatronic dinos could be scary to kids as well as the big drop at end.
Jurassic Park Discovery Center - Indoor interactive exhibits like at Epcot (indoor educational exhibits on Dinosaurs) not scary, really cool cute baby animotronic dino here as well.
Pteranodon Flyers - NA - sit down zip line type ride for younger kids, very high up if scared of heights, otherwise not scary.
Toon Lagoon:
Dudley Do-Right's Ripsaw Falls - Splash Mountain
Popeyes & Bluto's Bilge-Rat Barges - Kali River Rapids (much longer and much much wetter, you might as well have jumped in the pool with your clothes on, we wore ponchos and still got soaked, water comes from below, above, behind, and all around you. Kali is a tame baby in comparison.) Only scary if you are afraid of getting wet.
Me Ship, The Olive - NA - play area where you can shoot people floating by with water cannons
Marvel Super Hero Island:
Doctor Doom's Fearfall - Tower of Terror - (outdoor, very tame in comparison, only drops once) Still high enough to be scary if afraid of heights. I like it ok, and I hate ToT which I find painful, so ...
Storm Force Acceleration - Tea Cups (very mild X-men theming)
The Incredible Hulk Coaster - NA - outdoor coaster goes upside down
The Amazing Adventures of Spider-Man - NA - similar to FJ and Transformers, can’t remember how scary, sorry. But expect it to be an intense sensory experience with things happening all around you, lights, screens, animatronics, fire, etc. Ride vehicle is the same as Transformers, so if one makes you motion sick, the other probably will as well.
Universal Studios - Florida
Production Central:
Shrek 4-D - A Bug's Life or any other 4D theater show at Disney, kind of had a darker storyline than the other kids shows like the Minions, could be iffy. Sorry, can't remember details. I just remember it being kind of dark with some scary theming.
Despicable Me Minion Mayhem - NA - closest to any of the 3D/4D theater shows but if you were sitting in seats that moved similar to the Star Tours ride. Nothing really scary here unless the movie scares you. I also think there were a few non-moving seats available.
Hollywood Rip Ride Rockit - NA - outdoor upside down coaster set to your choice of soundtrack
Transformers - NA - closets to Spider-Man or FJ
There are lots of big lifesize transfomers fighting (both 3d animatronics and on screens), things explode, real balls of fire come at you where you can feel the heat, loud noises go off, it is pretty intense. Motion wise it didn’t bother me, but I know it does some people.
New York:
Revenge of the Mummy - Cross between RnR and Dinosaur (indoor dark coaster with Mummy Storyline aspects to it) I’d say too scary. It is dark with scary Mummy movie aspects. I also thought it was very jerky and painful. It made me kind of sick. And we came to a very abrupt stop at one point which threw me forward very hard, something that didnt need to get squished, got squished, and that was the last straw for me. I don't do jerky rides.
Twister...Ride It Out - NA - indoor recreation of a tornado with real wind and rain. This can be intense. Some of the younger kids were scared because the wind is blowing stuff all over, knocking down big stuff, thunder, lightning, things coming at the audience the tornado picks up, etc.
San Francisco:
Disaster - similar to parts of the Backlot Tour (to the acting / filming part at beginning and some of the special effects parts during the tram ride; however, there is no tram or ride, you are suppose to be filming a disaster movie trailer which they play for you at the end, they take volunteers for parts, just like the Backlot Tour does as well.)
World Expo:
Men in Black Alien Attack - Buzz Lightyear but with scarier things to shoot at. I could see how kids could be scared of the aliens. They are just the aliens from the movies, though.
The Simpsons Ride - Star Tours (with fictional theme park setting, like you are riding through on the different rides) Haven’t gotten to do this yet, so not sure about how scary it is. I’d say if you can do Stars Tours, you should be fine motion sickness wise. They are the same ride vehicle. The storyline is you are riding the fictional Simpson theme park rides. Scariness factor would be some of those rides breaking down and taking you to hell.
Woody Woodpecker's KidZone:
Woody Woodpecker's Nuthouse Coaster - Barnstormer (kiddy coaster)
Fievel's Playground - Honey I Shrunk the Kids Playground (outdoor play area with same giant scaling, plus splash areas, and a small water raft slide)
E.T. Adventure - Peter Pan (but you sit on flying bikes) Is dark inside, but not pitch black, so the neon paint shows up, but not scary, unless you are afraid of heights.
Animal Actors on Location - Flights of Wonder (with more animals than just birds, dogs, cats, raccoons, otters, etc., they do a variety of different tricks, some audience participation parts for kids and adults as well)
Curious George Goes to Town - NA - interactive outdoor playground with splash sections
Hollywood:
Lucy: A Tribute - Walt Disney: One Man's Dream
Universal Orlando's Horror Make-Up Show - ? Have heard this is very gory and can scare small children. I have no desire to see a show on how to make a person look like their arm has been sawed off or the equivalent, so I’ve not seen how bad it actually is.