Linda,
So the best route is to take the monorail or boat to the Magic Kingdom, then from there the boat to the Fort Wilderness marina. It is both a convenience and an enjoyable trip as well. That will drop you off right within walking distance to the
Tri-Circle-D Ranch for pony rides.
As for the
Chip and Dale Campfire Sing-a-Long, that probably will require you to hop on one of the internal bus routes to get there. I think it was the Yellow route.
Regarding the stroller, I would definitely take it along. It will make getting around much easier. And getting it on and off the boats should not be too onerous.
Finally, regarding snacks, there are many options. Near the marina there is Crockett's Tavern and Trail's End Restaurant. Of course the famous Hoop Dee Doo Review, as well as Mickey's Backyard BBQ are there as well. For more snacking needs, there are several options, like the Chuck Wagon and Meadows Pool Snack Bar. I don't think you will lack for plenty of options for a quick bite along the way.
Glad to help out!
Have a magical vacation!