We did US/IOA in August 2007 with a 3.5 y.o. and a 9 y.o. who is very petite and timid. The 9 y.o. was tall enough to ride everything except Hulk, Dr. Doom and Dueling Dragons (all in IOA). She was a bit nervous on a couple of rides but ended up liking all of them, except for Earthquake and Terminator.
Since the 7 y.o. is timid there are a few rides I would do child swap on first in Universal Studios to see if you think its ok for them. They are The Mummy (inside roller coaster type ride, doesn't go upside down), Men in Black (similar to Buzz Lightyear), Earthquake (now Disaster - similar to the Back Lot Tour) and Terminator (3-D movie/show).
In Islands of Adventure Dudley Do-Right is similar to Splash Mountain, but it has a bigger drop, Popeye is similar to Kali River Rapids, Jurassic Park is kinda like a cross between Dinosaur and Splash Mountain. There's really nothing to compare Spiderman too (and its awesome, one of the best rides in Orlando).
Suess' Landing in Islands of Adventure is great for little ones. Some of the best theming I've ever seen. My niece also really liked the playgrounds and water park areas. There was lots to keep her entertained.
Make sure you see the Animal Actors show at Universal Studios (the kids loved this). They also really liked the Sinbad show in Islands of Adventure (the little one absolutely loved it - I think we saw it at least 7 times while we were there).
Hope this helps.