I would consider a trip to DHS because they have a bunch of great shows including Playhouse Disney, The Little Mermaid, and Beauty and the Beast
As for USO/IOA, I am thinking one day might work since IOA will be the park to go to!
Do you kids do rides? What are your kids' preferences in parks? Personally, my mom took us on everything (whether we liked it or not, lol).
They like rides but even my 4yo still prefers the very little kid rides. He will do tea cups usually, loves Dumbo type rides but has not done a coaster b/c he is not a daredevil at all. And I would not make them do anything b/c it will ruin our day with hysterical crying. And they LOVED the Pets Ahoy show at Sea World. So to answer the question, they really like shows (we live near Sesame and they love their shows) but they are limited in how many shows they can do so we are usually best just doing one real show in a day.
I think that if we do DHS then we would probably skip Universal this time, might just buy a 4 day pass and spend 2 days at MK, 1 at DHS and 1/2 at Epcot. Is there anything to entertain them at Epcot? Now that I think about it I think my son would like it b/c he is obsessed with maps and globes right now but not sure what there is to do for them there. But DH would love to eat at the English restaurant.
When he was 18mo, we did all the parks, Disney, Universal and Sea World but we had 2 weeks to work with. The one bit of advice I can think of that'll help is, "think small." The littlest things draw their attention, remember they're only a few feet from the ground.
Water seems to draw them, whether it's the squirt up fountains at Universal or the misters at Disney. Zachary loved playing in the sand area at Sea World. So you see, it may not be rides that make them happy but the simple things.
I believe Disney's ride policy is that they must be able to sit up all by themselves so most of the tame ride are fine, Zachary loved them all at each age he went. Pirates of the Caribbean is fine, just have them close their eyes when they go in the dark areas and warn them about the drops. Try the Country Bears show and don't forget the parades and fireworks. Your son should love Buzz Lightyear.
Don't forget the meet and greet areas and if you want to blow some money, take them to one of the restaurants that have their favorite friends come by while you eat. Just remember to take it slow and stop for a nap time if they need one. You never get your money's worth when small ones are around, so don't try to cram to much into the trip. Think of it as THEIR trip, you'll have plenty of time latter in life to enjoy things with them, like I'm doing now with Zachary since he's 12yo.
Toy Story Mania at Hollywood is a great ride but I don't know what the height requirement is, your son should make it. I'm making this to long, so enjoy you trip.
Bobby, formally known as Bob & Robert!!!!!!!
And I agree about thinking small. I was very proud of us last year when we went because we totally followed their cues and did not push them much beyond their limits. For example we ate dinner at Sea World at 5:00 and then went back to the hotel. At MK and AK we probably only lasted until 4. And they did love the water area Sea World, no sand though.