[rafjen]

We have taken our kids to Universal since the youngest was 2. They love it and loads to do.
Parent swap is a bit different as you all queue up and wait in a special room usually with a cartoon/film showing and with air con ( bliss). My kids love the MIB one as they can watch the ride load. Bring in your drinks and some snacks and you are sorted. Also means no lockers. Personally I prefer this to the Disney child swap.
A 3 year will love the Hogwarts express itself.
Seuss landing is brilliant for kids and the character interactions there are the best we have had ( including Disney). Read some of the books before you go.
If they love dinosaurs the Jurassic park areas great.
The animal actor show is likely to appeal to younger kids.
At 3 my son was happy taking it all in and didn't mind not actually riding all the rides.
Now at 6, 9 and 11 they are my kids preferred parks.
My kids loved the Marvel character meal- food was only ok for the adults ( kids loved it) but the interactions were great.