For that age group, I'd choose Blizzard Beach. Both water parks have great areas for the whole family, special areas for the smallest children, and amazing slides for older daredevils, but only Blizzard Beach has a special zone for older children. This area, called
Ski Patrol Training Camp, is a HUGE favorite of my children (also an older child with younger twins). They LOVE the zip line ride over, and then into, the pool. And they can spend hours trying to cross the "river" on giant chunks of "ice."
And don't forget to try the
Teamboat Springs Family Raft Ride. In the attraction, your entire family can sit together in one giant raft while racing down a twisty turny terrific water slide. Hands down, this is my family's collective favorite attraction in all of Walt Disney World. We all have other favorites, but this is the one that we most like to do TOGETHER.
Enjoy!