When I took my daughter to Sea World she loved looking at the large manta rays. 
I love Sea World!  I've been many times, and I love to see the dolphins!
I love the dolphins the whole marine and oceanarium at the theme park is not only educational but very fun for kids even us adults lol.
It's fun for everyone!  I usually go to the Sea World location in Orlando, Florida - we go to Disney World as well!
I love Disney we go to Orlando, FL as well being we live in Florida so it is very close, Disney World is just so magical I can't wait to take my daughters there to enjoy the park.