We've eaten at all three and would <i>definitely</i> go back to all three.
Gaylord Palms is within easy access of WDW, situated at the junction of Osceola Parkway and International Drive, at the bottom right-hand corner of WDW (just outside its perimeter). Osceola Parkway runs east to west along the bottom of WDW property, the main landmarks being Animal Kingdom Lodge and Animal Kingdom to the west, Wide World of Sports and the new Pop Century Resort further east towards Gaylord Palms.
Sunset Sam's Fish Camp is in the 'Key West' area of the hotel. The restaurant is part 'harborside' and part aboard the 60' sailboat. We ate lunch on the sailboat. The dinner menu offers more options than the lunch menu. Kids would certainly be fine here at lunch and, I would imagine, at dinner too.
Villa Del Flora is one of the best buffets we have experienced in Orlando. It is in the St Augustine area of the hotel. Again, we ate lunch here. Not a place I would choose to eat dinner, but would be ideal for young children.
We had dinner at the Old Hickory Steakhouse in the Everglades area. We loved it, and will definitely return sometime. I wouldn't choose to take young children here. I would say it's quite upscale, along the lines of California Grill, but without the 'buzz' - much more subdued.