You got some good answers, but I was going to add that the only park that takes you to other parks is Animal Kingdom. I've never seen a park to park bus at other locations. However, if you wanted to go from DHS to Magic Kingdom, you could take the bus to the Contemporary and walk. Or vice versa. Walk to the Contemporary and take a bus to DHS.
The idea of no park to park buses seems kinda crazy with how they push adding park hopping. We've set on just driving the whole time now. I don't think it'll take too much time.
If I had a free evening at Disney World with two little boys, I'd do one of two things:
1. Eat dinner at Captain Cook's at the Polynesian, let the boys play in the sand on the beach, tour the monorail resorts and check out the Christmas decorations at each, (maybe include some sort of a game, like buying a cookie or trinket at each resort), and if there was any time left, we'd take the boat over to Fort Wilderness for the bonfire.
2. Eat dinner at Mara at Animal Kingdom Lodge, explore the resort, maybe find a playground, see the animals through night vision goggles, sit by the fire-pit, and get lots of zebra domes, which I haven't had before, but I'd love to try some.
Meeting Rapunzel and Flynn looks like it was a cool experience, although an hour and a half still seems a bit daunting to me. It was nice that you and the boys got to go on some rides, though. I do wish Flynn was still there.
Yuck to sand.

Those both sound fun though. I remember looking at the Chip & Dale campfire thing before, but didn't know if it was open to everyone or just those staying there. I'll read up on that!
I thought the wait was nuts for Rapunzel, so it was super nice that John held the spot instead. I'm glad we did it for them to meet the characters anyway, especially with Flynn gone now.