With younger kids we like the The High in the Sky Seuss Trolley Train Ride, The Incredible Hulk Coaster, One Fish Two Fish Red Fish Blue Fish, and You'll Get Wet. Those are nice and only the Hulk Coaster was over the top scary. I would go early, as it is a late arriving crowd. You will certainly want to take the big challenge and do the Doctor Doom's Fearfall, Dudley Do-Right's Ripsaw Falls, and the Dragon Challenge. It is so fun!
My ride pick at Islands of Adventure is The Incredible Hulk. Before you go on The Hulk take a shot of vodka as this one launches you upward 150 feet, very scary, and reaches top speeds of 65 mph. It seems much faster and it has seven total inversions, so this is not for everyone. Very fast and lasts for about two minutes, which seems like five.
The park kind of forces you to buy the Universal Express Plus Pass if you want to ride all the good stuff in one day. Getting express ride access seems like a money scam, but it works, as most people do not buy them. It works the same in both sides of the theme parks.