We have stayed at both. We love POR. The Polynesian is nice since it is on the monorail. With little ones this can be a plus. But I think that the niceness of the Polynesian would be lost on the kids. The pool at POR is very nice. You know,,,,it's funny but last summer we stayed at the Polynesian. This was my dd's biggest wish. She loves POR but for some reason she really wanted the Polynesian. When we got a terrific rate at the Polynesian we grabbed it. Well. My dd didn't seem to be so happy when we got there. I asked her what the problem was. Her answer?? "It just doesn't feel as magical as POR." I think that was because POR was the only place she had stayed.
Now, the Polynesian has two queen size beds and a daybed that is a twin bed. The rooms are bigger than POR. POR has a big food court. Polynesian doesn't. But it does have a smaller court type restuarant. The pool at the Polynesian is zero entry which is nice. Both have pools for little ones.
Would I upgrade? Probably not. But that's just me. I love POR. If you do decide to change, you would have to do it with your TA. It's really not something I would do at arrival. There may not be any rooms open for your travel times at the Polynesian. Check with your TA and see what the difference would be. Good luck with your planning.
And welcome to the DisBoards!!!