Hi Jamie!
My immediate response is Fort Wilderness, but I surveyed my kids to see what they would say. They are 6 and 3 and in unison chanted, "cabins!".
Disney's Fort Wilderness Resort & Campground is such a gem and is completely different than any of the other resorts at Walt Disney World. The entire resort is surrounded in nature and just has such a relaxed vibe to it. It's easy to forget that you're just a boat ride away from the Magic Kingdom. There are so many activities, including our favorite, Chip 'n' Dale's Campfire Sing-A-Long. This is definitely a resort where you'll want to plan some time to actually enjoy the amenities it has to offer it's guest. For a little extra fun, reserve a golf cart for your personal transportation around the resort.
Disney's Caribbean Beach Resort is a great moderate resort. The biggest draw for us is the Fuentes del Moro Pool that is themed like a Spanish fortress. If your son is into swashbuckling adventure, this resort is home to the
Islands of the Caribbean Pirate Cruise (although you do not have to be a guest at this resort to enjoy this) that is just for kids ages 4 to 12. The kids board a vessel with an adult crew and set sail in search of treasure. My son has done the Pirate Adventure at the Grand Floridian twice and still can't stop talking about it. This is an extra cost and reservations are highly recommended.
As you can see, my vote is heavily towards Fort Wilderness, but you are sure to have a magical vacation no matter the resort you choose.
Have a magical day!
Leslie