With 4 adults plus a three-year old, you can stay at:
Family Suite at ASM
Alligator Bayou room (w/trundlebed) at POR
YC/BC
BWI
GF
Poly
CR
deluxe rooms at WL or AKL
Since you mentioned that your dad and DH are big guys, keep in mind that the beds at POR are doubles, not queens. Not sure what the bed situation is in the Family Suites.
You could also consider renting a 2-bedroom villa at any of the DVC resorts. That would give you one king bed, one or two queens in the second bedroom, and a sofabed in the living room. Not to mention, a full kitchen, two bathrooms, a washer/dryer, and lots and lots of room.
You can book a villa through CRO as you would for any Disney resort, or you can rent a reservation from a DVC member, which will cost considerably less, but will likely have much stricter cancellation policies (i.e., you may not get your money back if you cancel). If you're interested in renting, be sure to read all of the FAQs on the DVC Rent/Trade board to make sure you understand the process, and how it differs from booking a room through CRO.