Just a short walk up from the Marina you will find Cinderella's Pony rides. Forget the fee off hand but that it is reasonable. The Barn is just beyond that and you may be lucky enough to be there as they are grooming /bathing one or more of the Percherons getting ready to go on stage at MK. You can also take a walk through part of it and check out their accommodations and see one or two up close They also have the Calliope from the parks early days and a nice exhibit showcasing some of the important horses in Disney history.
At Pioneer Hall you might get lucky and find the checkers game free. The rocking chairs are a good place to sit back and people watch for a bit. There is even a thread here dedicated to Kicking it at The Fort, But the rules for posting are rigidly enforced with signicant penalties for violations.
You can also take a bus up to The meadows complex where you can rent bikes, canoes, Kayaks ,and Cane Poles for fishing in the pond area. There is also a play ground here like down by the Marina. Or you can continue up to the Outpost where the Trail Ride is This requires a reservation and cost $55 per person for a 30 to 45 min ride. Others may have a more detailed listing.
Now should your boy's be extremely adventurous and you are willing to risk them, you can always tell them that Ft Wilderness is Home to The Ninja Squirrel Squad (NSS). Mind you that they did eventually find the last group that went looking for it.