Hi Ashley,
Sea World is a beautiful place to spend a day with your family. My two boys love ocean life, and enjoy taking an excursion off Disney property to visit when we are on vacation. They especially love the attraction that allows you to feed dolphins. We have some amazing pictures of them doing this!
There are number of options for spending a day at Sea World.
You can rent a car, for any length of time (including one day) on Disney property from Alamo or National at the Disney Car Care Center (407-824-3470). Free shuttle buses run from the Disney resorts to the Car Care Center. If you prefer not to spend money on a rental, you can use the LYNX Public Transportation Bus System and catch bus #50 from the Ticket and Transportation Center (TTC) to Sea World. Buses run throughout the day. Reviews on the "ease" of using the system are mixed, as you have to factor time to get to the TTC, stops along the way, etc. The trip can take you well over an hour each way. You can also hire a taxi, which are generally available outside the main lobbies of all of the
resorts. If taxis aren't waiting, you can ask the front desk to call one for you, and they'll be happy to do so. You can also use Mears Transportation Service by calling 407-423-5566 for reservations and current prices. Presently, the cost is $18 per person and kids under three are free. Mears can make arrangements to pick you up at Sea World to return you to your resort as well.
My vote for the most convenient way to get to Sea World would be either Mears or a taxi.
Have a wonderful vacation!
Tanya