I think the biggest mistake is not giving it a shot. How will you know if you never go?

I'm sure you'll want to limit your stay at US/IOA and keep your Disney trip long, that way, if you are unpleased with what Universal has to offer, you still have WDW to look forward to!
someone made a comment about there not being much for young kids to do at Universal. I strongly disagree with this, but I guess comparing it to Disney, it may be true?
There is a section in Universal Studios called KidZone. Name says it all. They have the Animal Planet Live show, ET's Adventure ride, Barney Show, Curious George Play Area, Fieval's Play Area, and Woody Woodpecker's Kiddy Coaster.
But then....you have Jimmy Neutron's Nicktoon Blast and Shrek 4-D which may appeal to the younger kids. If they aren't big enough to ride, there are stationary seats available, so they can still enjoy the show. They have a Nickelodeon Studios Show/Tour thing for Nick fans.
In addition, there are many other shows at Universal. Extreme Ghostbusters, Street Breakz, and Blues Brothers are kid-friendly. Beetlejuice's Graveyard Revue and Horror Makeup Show have a PG-13 rating, but some parents believe this isn't an issue (in their case).
Don't forget character meet and greets!! From Spiderman to Spongebob, Scooby to Cat in the Hat!
IOA offers some fun play areas, including If I Ran the Zoo, a small water play area, that's colorful and FUN (kids of all ages enjoy this. I had a blast back when I was 12-years old...4 years ago!). Also in Suess Landing is a Caro-Seuss-el...a carosel (sp?) made up of Suess characters instead of horses. One Fish, Two Fish, Red Fish, Blue Fish is similar to Dumbo at Disney..only the fish can squirt water. There is Cat in the Hat ride, which is very cute, and tells the story of the Cat in the Hat.
Jurassic Park area offers some VERY nice play areas. Plus a special ride JUST for kids. Yes...kids have to ride with an adult, however an adult cannot ride without a child. lol. This is the Ptronadon Flyers (sp?). There is also a kiddy coaster at IOA called the Flying Unicorn.
But most of all....see the Mystic Fountain! This is a hit with many kids. The fountain interacts with people...adults and kids alike. But be careful, for it may squirt you with water!!!
I think you will all enjoy it. Expect it to be completely different from Disney. Completely. US/IOA are great parks....I'm sure you'll have a great time!