Hi Tracey:
My family always uses Disney's complimentary airport transportation between Orlando International Airport and our Disney Resort, also known as
Magical Express. My whole family enjoys the entertaining "welcome" and "goodbye" videos shown on the bus that feature our favorite Disney characters. The service is operated by Mears Transportation. Mears
does not permit car seats on Magical Express, nor are they apparently required to permit them. In any event, the buses have no seat belts or other restraints to secure the car seat, so a car seat on the bus would likely have limited safety value.
I feel comfortable with my young children on Magical Express, but your family has to make the decision for themselves. One alternative to Magical Express would be to rent a car and either bring your own car seat or request a car seat add-on from the car rental company. If you decide to utilize Magical Express, my top safety tips would be to hold small children in your lap and avoid sitting in the first row of seats on the bus, as this row does not have seat backs in front of them that can be used as a brace for any unexpected short stops.
Enjoy your vacation.