The Beach Club is a GREAT resort. My family has stayed there nearly a dozen times and we have another stay booked there in November. You can read my recent analysis of the Beach Club versus Polynesian question
HERE.
After reading that, here are some additional things to think about for your particular situation:
- I have never felt like the temperature of the Beach Club pool was any different than the other Disney hotel pools. I've swam at the Grand Floridian, Contemporary, Boardwalk, Animal Kingdom Lodge, Wilderness Lodge, and several others. The temperature seems quite constant at all of them. The WDW resort pools are all heated year round.
- At age 3 and 4, I simply could not drag my kids out of the sandy area of the BC pool. They loved every second of it. This is one of the few opportunities that kids have to build real sand castles that won't get washed away by the tide.
- On the pro-Poly side, if your family spends most of its time at the Magic Kingdom, then the convenience of the monorail is hard to overlook.
- There are wonderful aspect of all the WDW resorts. Most of the Moms on the Panel really love learning about the great nuances of each of them. You have to decide whether you're most comfortable with a known quantity (the Poly) or branching out to try new things.
Good luck with your decision.