My kids prefer IOA to US. They were this way even before the Harry Potter area opened up. We haven't been to US since they were much younger though - the last time they were 11 months, 3, and 6. The last time they did IOA, they were 2.5, 5, and 8. My oldest loved IOA even at 3 years old though! We're planning a trip next month though and will be spending multiple days at both IOA/US. I'm figuring my kids are now old enough that US will last longer. (They're 4, 7, and 10 now). On that trip when they were 11months, 3, and 6, we spent 1.5 days at IOA and 0.5 days at US. We could have easily spent longer at IOA but half of a day was enough for US at those ages. If you have the time and money, then I'd suggest a 2 day park hopper so you can do both parks. And if there's not enough in one park, then you can head to the other.
As for what they liked:
IOA
*The kiddie coaster in the HP area, Flight of the Hippogriff. My oldest did Forbidden Journey on the last trip and liked it okay, but it bordered on too intense for him. They loved the shops, but they do like HP. Definitely try some frozen Butterbeer even if you're not HP fans!
*Spiderman. It's a 40" ride so I'm guessing both of your kids are tall enough.
*Dr. Suess area - they liked all the rides in that section and the play area- even my oldest who was 8.5 on our last trip there.
*My two boys have some sensory issues and as a result, we did not do the water rides with them. But, a lot of kids love water rides and there's several of those. Just make sure to bring extra clothes!
*Storm Force Accelatron - It's like the teacups. I can't handle this one due to motion sickness, so I send hubby on it over and over and over.
*Sinbad Stunt Show - They loved this show.
*The storytime was really enjoyed by my younger two. My oldest pretended he was too cool for it. We were able to meet some characters up close and without crowds, which was pretty neat!
*Poseidon's Fury - They liked this okay. I'm still partial to the way it used to be, but it's still worth doing.
*The water fountain - There's a talking water fountain which is lots of fun. We've hung out there for a looooong time before since it's so much fun!
**The only attraction I'd recommend skipping in IOA is Pteranodon Flyers. The loading time is terribly slow and it's not that exciting of a ride. So, I'd only do that one if you have extra time and the line is short.
*Camp Jurassic - It's a play area but not a really little kid area. The 5 year old will be fine with an adult. My oldest could spend all day in that area and be happy.
US
It's been a while since we've been so there are some new attractions and some my kids weren't ready for before that they're ready for now. Go to the website to read up more about the attractions/shows, as it's been a while since we've been.
*Men In Black - That was one of my oldest's favorite rides at 3.5 years old. It's like a faster/darker Toy Story - you shoot at aliens.
*Terminator 3D
*Shrek 4D
*They loved Jimmy Neutron and that ride has changed to Despicable Me. It's still the same idea though, just a different movie on the screen so I would suggest that as well.
*Mummy - This surprised me since my oldest is not a roller coaster kid and usually refuses to go on the bigger rides. But he enjoyed it!
*Simpsons - Oldest liked it at 6 but it totally freaked my middle child out at 3. Though it's a cartoon, it felt like she was really crashing into the wall to her.
*We're looking forward to the Transformers ride, which we haven't done yet.
*There's also several shows, which we didn't do since our kids didn't have the attention span when we last went 4 years ago. The Animal Actors one is supposed to be the best of the shows for kids.
*Curious George playland - They loved this area! There's water to squirt but there's also a building with balls to shoot out. I'm not sure if you've ever been to Stone Mountain in Atlanta, but similar to The Barn there. Curious George sounds like it's for little kids but my 10 year old will still likely enjoy the ball building.
*There's also a little magic shop that advertises magic shows. They do try to sell you the materials after the show, but it was really well done and we enjoyed it.
