Unless they're up for anything they may find most of Universal and IOA to be too much for them - which may bring "value" into the thought process. Many of the rides at these parks fall into the thrill ride category and they are a lot of fun but generally more aggressive that the Disney thrill rides. The Dr. Seuss area of IOA would likely be perfect for your children - Hat In The Hat (similar ride to Disney's Snow White ride in MK, themeing is wonderful), One-Fish-Two-Fish (something like Dumbo, but with water squirting), there's a great Seussian carousel, and Seuss characters. The Jurassic Park section has a rather extensive playground area though I'll admit that when my youngest daughter was young enough to play there during our first visit I thought that it was difficult to keep track of her because of the layout and it was pretty crowded. The big ship in Toon Lagoon is fun, too.
In Universal, Jimmy Neutron is a motion simulator that's pretty jerky (the motion of the ride, not the quality of the show) and has a height minimum of 40". Shrek is a dark 4-D show and they really pack people in in the pre-show room so the crowding and darkness could be pretty intimidating for small children. The Woody the Woodpecker area is designed for the youngest guests and has some neat things to do - there's a themed playground area, a Curious George play area, a Barney song-fest show (do they need to update the characters so they're more recognizable for the little kids?), and a kid-sized roller coaster. Universal is a great walking around theme park as there are street performers in addition to the Blues Brothers show and you'll see the occasional character parade.
I'd suggest that you ask questions about Universal/IOA at the Universal forum that down toward the bottom of the list of forums here. And also go to the Universal Orlando website to see what might be appropriate for your family -
www.usf.com or
www.universalorlando.com.
You might think about SeaWorld as an alternative, too. There's a lot to see there while not a lot in the way of rides (most that are there are thrill rides). But the shows are absolutely incredible - don't miss Believe if you go.
www.seaworld.com
If you're up for the 60 - 70 minute drive to Tampa then you could also consider Busch Gardens. A nice mix of rides (while the big coasters dominate visually, there are other more tame rides too), shows and animal attractions. This was our favorite park on our first visit to Orlando some 32 years ago, but then Disney World consisted only of the Magic Kingdom back then.
www.buschgardens.com/BGT
Try a Florida state park like Blue Springs state park that's located in Orange City and easily accessed by taking I-4 East. I'd guess that Orange City is 45 minutes or so north of Orlando. For me, the big features of Blue Springs are the manatees that winter in the springs every year. It's really something to see them in a safe, natural setting.
www.floridastateparks.org/bluespring.
A non-theme park Disney side trip might be to go to Downtown Disney. The Legos store is always fun and I'd try the new T-Rex Cafe (it's owned by the company that runs the Rainforest Cafes so the themeing should be pretty good).
Dick Taylor