If you can only do one of the Universal parks, with kids that age I would hit Universal Studios. Woody Woodpecker's KidZone is a very large area that makes up one whole area of the park. At the entry is the Animal Planet show which is delightful for kids and adults, too. Also the ET Adventure is at the front of the KidZone. Fievel's Playland is a kids play area with a small raft water slide. (Lines can get long later in the day.) Woody's Nuthouse Coaster is a smaller, family coaster (Think Goofy's Barnstormer at MK). A Day in the Park with Barney is delightful for the little ones (although your 7 y/o son may be rolling his eyes at Barney by now

) Inside the Barney attraction is a small indoor play area which is nice in the heat of the day. Then in the very back of the KidZone is Curious George's play area. Bathing suits are a MUST here. Once your kids see this area, you will be here for the rest of the day. Behind the wet area is the ball factory, which dads seem to like a lot too!
The kids will also love Jimmy Neutron and Shrek but make sure to do these first thing in the morning or the lines will be prohibitive. Nickelodeon Studios is down the street from Jimmy Neutron. The Nick characters are out and about at various points during the day. I'm sure you're boys would love MIB, but they must be at least 42" to ride. Otherwise there is a baby swap area.
BTW, here are the height requirements for the attractions:
UNIVERSAL STUDIOS®
Revenge Of The MummySM- Must be at least 48".
Jimmy Neutrons Nicktoon Blast- Must be at least 40. Persons under 40 must experience this attraction from an adjacent stationary location.
Back To The Future The Ride® - Must be at least 40 ; 40 to 48 must be accompanied by an adult.
MEN IN BLACK Alien Attack - Must be at least 42 ; 42 to 48 must be accompanied by an adult.
Woody Woodpeckers Nuthouse Coaster® - Must be at least 36 ; 36-48 must be accompanied by an adult
Islands of Adventure is a wonderful park and is my family's favorite but I really think younger children will enjoy the Studios more.
Have fun, whatever you choose.