We did the Arctic Expedition tour at Sea World with our then 4 yo son, and he liked it alot. They took us behind the scenes, and gave us some information on the colder climate animals, at the end of the tour you get to pet a penguin (a staff member is holding it). My son has autism and did very well with it. I am sure they have other tours, this is just the only one we have done so far. It was reasonably priced too. If you go to SW and are animal lovers, don't forget to check out the Pets Ahoy show.
Our favorite tours have been the ones at Busch Gardens in Tampa if you get that far off the beaten path

They have a few tours that allow younger children, we have so far done two that include giraffe feedings, and we all (DH, DS and myself) found it an awesome experience. They have others we hope to try in the future.
I don't think Disney allows young children on any of the animal related tours other than the Sunrise Safari, which requires staying at AKL (concierge I believe). We haven't done it yet because we are waiting until construction is finished there before we stay there. I expect that since it is Disney, they are probably pretty strict about ages, I really do wish Disney offered more in the way of animal experiences for families with little ones.