I would go with the cabins. Our kids were 9 & 10 on our first trip (9 nights) and they never thought twice about FW not being 'Disney enough'. The parks themselves were overwhelming enough, a little sensory detox was actually kinda good for them. With yours being much younger, I can't imagine they'd notice at all. We enjoyed going to the outdoor movies, and the kids loved chasing the little lizards in the woods. Our driveway was lined with pine cones -- it was just all so peaceful and perfect. If you're going to spend lots of time in FW, I'd rent one of the golf carts -- your kids are kinda little to walk a lot. Our kids rented bikes and loved it!
Also, its real nice having the separate bedroom -- can put the kids to bed and close the door and still have some 'grown up time' in the rest of the cabin...
If you go during the holidays, take something to decorate your front window. We were there for Halloween, and didn't know to do this, but almost all the cabins had pumpkins glowing in the windows. It was too cool.