Hi Julie! I think your children will have a blast if you can fit these activities into your schedule!
Mickey's Backyard BBQ starts at 6:30 p.m. and will end around 8:00 p.m. You'll want to make your reservation as soon as possible as this is a very popular event!
Chip 'n Dale's Campfire Sing-A-Long typically begins at 8:00 p.m. (please double check the calendar for your specific travel date) and if you'd like, you can purchase a S'mores kit for a nominal fee. After the sing-along (which lasts about 40 minutes), your children can enjoy a Classic Disney Movie.
Transportation to Fort Wilderness isn't that bad if you plan ahead and leave plenty of time for transportation. If using Disney Transportation, you could take a bus to Magic Kingdom and then transfer to a boat headed to Fort Wilderness.
When leaving Fort Wilderness, you'll want to check the time. If you time it before the last show of Hoop-Dee-Doo is over, you can head over to the resort buses to bring you back (ask a cast member for help on getting to the right bus). If the Hoop-Dee-Doo is still in session, you could go to the boat launch and head back to Magic Kingdom to transfer to a bus headed back to your resort. (Note: the boat launch gets quite crowded as soon as Hoop-Dee-Doo show ends which is why you'll want to be aware of the time when you leave. When in doubt, just ask a cast member for assistance.)
Have fun and have a wonderful vacation!