Hey there, William! Welcome to the Disney Parks Moms Panel!
Disney's Fort Wilderness Resort & Campground is one of my family's go-to spots when we stay on property. There's just about every recreational activity you can think of, from boating to horseback riding to fishing to bike riding to playgrounds to...well, you name it! And you're right, Fort Wilderness is enormous, so having a golf cart to get around to all those great activities is a big help.
The best way to rent a golf cart for your stay is to reserve it in advance, since they have been known to run out. There's more information about reserving golf carts on the Golf Cart Rental page on the Disney web site. If your time is short and you can't reserve in advance, they're available on a first-come, first-served basis at the Reception Outpost. Just let the Cast Member know when you check in that you'd like to rent a golf cart and they'll help you. If you can't get one for your first day, see if you can reserve one for the next day. You may have more luck as people return their carts at check-out.
I hope this helps you tool around in style at Fort Wilderness, William. Wishing you tons of fun in the wilderness!
Kathy K.