I just read a comment over on the Resort board... someone just got back from the Yacht Club, and they reported that the bus transportation was fine for them.
With pre-schoolers, the walk through Epcot and to the Monorail, switching at the TTC would be an extreme hassle...
I wouldn't worry about the buses. I've been doing a lot of Epcot Resort morning runs lately, and it's been fine over there.