Boat to MK, then monorail, or ferry, to TTC. The Lynx bus system will take you right to the parking lot for SeaWorld. It's about $1.50 pp each way...kids may be less, not sure. I believe it's the #50 route. It is right at the TTC. If you go to the Lynx site....
www.golynx.com you should be able to find a timetable. But, be sure to let the driver know when you get on that you want to get off at SeaWorld..he won't stop automatically! And bring the correct change.