You will be able to swim at Thanksgiving time. All the pools are heated too so even if it’s a little cooler, you can still enjoy.
I think either resort will be great for that age.... my dd is a terrible swimmer and she had a really great time with the pool slide, sandy beach area, whirlpool etc at the Beach Club. As for the Boardwalk, the atmosphere & design is quite whimsical. Little girls love it. These 2 resorts are our favorites and have stayed at both multiple times. We usually base our decision on where we can find the better price.
I will say that we have a hard time convincing my dd not to spend all her time at the pool when we stay at BC/YC. Something to consider if you are pretty set on your game plan