OK, I loved Universal Studios (Florida) as a teenager. Now I'm a Mom and we're going for a weekend. With a 2 and a half year old and a 5 year old, I'm thinking that we'll be able to do both parks in one day b/c it just doesn't seem like there is much for them to do. I mean, they'll have fun I think, but will we need to spend 2 days?
If you have been with kids these ages, what was your children's favorite part?

Sorry for the long post. There aren't as many people on the Univ board so I like to be helpful.


We've been the same situation a couple times (I now have three kids 6, 4, and 1). The most specific experience I can give you was when my son was 2 and daughter 4. We were very hesitant because we went to US/IOA at the beginning of our trip so this was the first theme park for my son and my daughter was finally old enough to really understand.

It turns out, the kids really surprised us at how much they loved it. Even more, Islands of Adventure was a huge hit and they talked about it more than our Disney days which really shocked us.

Most of the kid fun depends on what you like to do with your kids. Are playgrounds fun for you? Are you willing to go on the rides you like and baby swap the kids?


General Advice
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Our approach to theme parks is we go on every ride we adults want to and we mix in a kid attraction between each ride. In the end, we spend more time at theme parks than if we were alone and we don't skip anything.

We love the interactive playgrounds with the kids because we like to take video and photos. Sometimes one of us will go on an adult ride while the other is doing playgrounds (get a baby swap pass from the cast member).

You have to gauge the kids' excitement tolerance. Our kids are really good but some kids have a hard time with thrill and loud noises.


So here is what was really fun for them and why we spent several days there by the end of our trip:



Islands:
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Flying Unicorn (kids coaster, has a 36" height requirement)
Pteranadon Flyers (you must have a kid with you to ride)
Seventh Voyage of Sinbad: good show, kids insisted we see it every day
Spiderman (40" requirement might be good for your 5yo)
Cat in the Hat: Obviously a big hit. It's a really good dark ride.
One Fish Two Fish
Carosousel
New Seuss sky train ride
Seuss plaground (bring a change of clothes if you let them get wet)
Popeye playground (man, this playground was a huge hit)
Playground in Jurassic is good.
Toon Town (if it's hot and you let them get wet)
Poseidon Fury (walkthrough attraction) -- only part the kids really liked was the water tunnel. Might be intense for some kids (fire and loud noise).



Studios:
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Woody woodpecker coaster (36" limit)
ET (4yo loved it but was confusing and the end was too loud for 2yo)
The Fieval playground near Woody is incredible though I had to help the 2 year old climb around. It was hot that day.
Curious George playground (could get wet)
Jimmy Neutron (has a height limit if you want to go on the moving cars)
Shrek (our first attraction). Our 2yo didn't want the glasses on. I'd say Shrek wasn't a huge hit.
Men in Black (42"), our 6yo loves this ride and now my boy is 4 he loves it
Jaws (kids didn't like it)
Earthquake and Twister (so-so, preshows are long)
Animal Planet (ok but not great like Sinbad show)
Barney (only enjoyable to kids)

The one thing that Universal seems to do better than Disney is playgrounds - Islands of Adventure has several well-themed playgrounds, and the play zone in the Woody Woodpecker area is fantastic too. (After visiting Universal, the Winnie the Pooh playground and the Boneyard may seem disappointing, although Tom Sawyer's Island is still the greatest playground anywhere.)

At the preschool age, I think playgrounds tend to seem better than traditional rides and attractions. You don't have to wait in a long line, and the fun lasts for as long as you want, not just for a 3-minute ride. For our 2-year old, the simple fire truck on Disneyland's Main Street that he can climb all over is much more fun than any of the rides!

I think you're safe either way. The kids would probably be satisfied with one day at Universal, unless you had to rush them off the playgrounds to get on the rides you want to see. If you went for two days they wouldn't get bored - they'd have more time to spend on the playgrounds, and would be able to go back to their favorite playgrounds and attractions the second day. (They do like repetition at this age!)