My niece is older than your kids, but SeaWorld had the same impact on her that it does on me. There's just no way to capture what it's like to see Shamu in Believe, plus we fed/pet the stingrays and dolphins.
Also, we did the Polar Expedition tour and there were about 10 small kids on the tour. They took us behind the scenes to see juvenile seals, polar bears, beluga whales and then we were able to pet a penguin. The small kids on the tour seemed to love it.