Check the park times. We were there in Sept. and the kiddie area at Universal didn't open until 11:00 or after. The timing of it's opening may play a big part in your choice with your time constrictions. There is not much else for little ones. Shrek and Jimmy Neutron, but that is about it.
Now, DD3 LOVED IOA. We spent 3 hours in Suess Landing. It does NOT take that long, but she wanted to ride things over and over again. She was just thrilled with EVERYTHING there.
Personally, we were disappointed in Universal but were very happy with IOA--adults and kids alike. However, we are just one opinion and you should definitely make your own.
Good luck and have fun!