With a six year old it may take a while to get to MGM, Epcot would be no problem, its about a 5 minute walk to the entrance, but then you have quite a walk to future world.
I've walked to MGM in about 15 to 20 minutes at an even pace. Taking the boats are slower than walking, but very relaxing. I found that in the evening it was faster to walk than to take the boats, especially after the parks close. One night I walked from MGM to the YC because the lines for the boats were horrible and I made it to the YC before the boats.
Coming from MGM the boats stop at the Swan/Dolphin first, and then I think they go to the Boardwalk and then to the YC/BC. I could be wrong about the order after the Swan/Dolphin because its been awhile since I stayed at the YC.