SW has some great things for kids of that age. Apart from the obvious shows which they seem to enjoy it's worth keeping an eye out for "Pets Ahoy" which is a bit "twee" for many adults but younger kids seem to love the different animals performing. Another easy to miss favourite is the "Tide pool" where kids can get their hands into the pool and handle urchins,sea cucumbers etc.
I think SW offers a really nice change from the regular "themepark" offerings , it combines some fun shows with hands on experiences ( kids ALWAYS seem to love feeding and petting the dolphins) and the opportunity to learn about the environment. It also has a great kids play area with loads ofthings for a variety of ages.
Hope you have a great day .