Our first trip to Disney, the kids were 5 and 7. Epcot was their favorite park.
Future World:
They loved Soarin and Test Track and Spaceship Earth and Innoventions at that age. We never got to Living Seas on that trip, but they really enjoyed it at 10 and 13 (and I would say it's designed for the younger set).
They tried Mission Space - Orange at 10 & 13 and LOVED it. I would have opted for the green version with younger kids since it's less intense. (This is the only REAL intense attraction at Epcot. The rest are tame by comparison.)
Club Cool is a lot of fun. Make sure someone tries the Beverly. (Insert evil chuckle here...)
There are interactive play areas in the Imagination and Mission Space buildings. My kids enjoyed these also.
World Showcase:
At 5 and 7, my kids did the Kidcot stops.
At 10 and 13, they did passports (we found on the Dis-igns board) and had a great time at each stop. The CMs would translate their name for them and write a short message. They also did a Kim Possible mission (now Agent P) and that was great for the age bracket your kids are in.
The street entertainment is nice because you don't have to wait in lines.

There are comedy shows, drum shows, music, and acrobats, which appeal to both young kids and adults.
Have a Great Trip!