Depending on what you mean by your kids being old enough for a waterpark, the following info might be helpful:
Blizzard Beach has a nice size area specifically for younger (elementary age - "tween" age) swimmers. It has two or three mid-size slides, a hang and drop slide, a pool, and iceberg balance-thing. It's a great place for kids old enough to want to play, but still hesitant or too short for the super-intense slides.
TL only has a toddler play area - nothing specific for ages 5-11.