Just returned from a 3.5 day trip to Universal. The fist day and a half, it was just my wife and I. The second day, we had our 2.5 year old daughter. To make a long story short, we learned the hard way that while there are indeed things that appeal to the younger set, Universal is at its heart a more adult-focused park, and not really ideal for a toddler. Some observations:
At UO, the whole Woody Woodpecker area is awesome. Our daughter thoroughly enjoyed Fievel's playland and the Curious George area. She could have spent all day there.
Unfortunately, with that said, that pretty much WAS her entire day because there's nothing else at UO that she could ride or that we would have wanted her to ride. Even the Shrek movie proved too intense, between the darkness, the loud noises and the moving seats. She did see Dora on her way out, which was a nice capper to the day, but we basically gave up around 1 pm and took her back to the room.
IOA was even worse. The play areas there are more geared towards older kids, and there are only a few rides that are options for the little ones at all.
Another thing I noticed that wasn't as apparent to me when it was just my wife and I was how little shade there was at UO/IOA. Jurassic Park has some nice shade, but most of the other areas are wide open to the sun.
Anyhoo, we loved our time at Universal, but we're definitely going to wait until our daughter is older and taller before we take her back there. As it was, we were basically going from ride she couldn't do to ride she couldn't do, in the sun, which made her fussy and made it tough for any of us to really enjoy the trip as much as we did a few days earlier at Disney.
Just wanted to pass along my thoughts for any parents of small children considering whether Universal would be a good fit. At least for us, it wasn't (yet).