LOL dvm, no we are not a member of the polar bear club! I just have a 2 year old who loves to swim and my 12 year old niece will be with us and she loves water. We might even try BB if it gets warm enough (high near 80, I think Sunday Jan 4th is forcasting it.) Anything that is comfortable to be outside is warm when you are used to Michigan in the winter. Today it was near 50 and I saw people walking around in short sleves.
The 1st time we were at Y&B we went in Feb for just 4 days (a mini trip since I was 32 weeks pregnant.) We really just wanted to hang out in the pool. A cold frount came by and it only got into the mid 50's most of the trip. The very last day the sun came out and it hit mid 60's. We got an extended check out and were in the pool until 1:00. (our ride came at 1:30 to take us to the air port.) I will admit it was a tad cool that day, but that is what hot tubs are for.
You will love SAB it is great for 2 year olds. The sand bottom wadding area is perfect for playing around, the hot tub is right near it so one parent can hand out there. One night all the other dad's around were joking they should buy my hubby a beer for wachting their kids too. Our DD and all the other young kids were having a blast builing a casltle in the shallow area and my hubby was right there leading the group. It was great fun. We are sad that we aren't at BCV this trip because we love SAB that much. (but we are looking forward to tying out VWL, our DVC home resort.) They have a nice little play ground too too. Y&B has a total of 6 hot tubs in the whole resort. 3 at SAB and one at each of the other pools. Eat at Beaches and Cream, we love that place. All in all BC is my favorite WDW resort, not only becuase of SAB, but many reasons. They sell some sand toys and the kids meal comes in a bucket with a shovel. At the end of the day their is 30 or 40 of them no one claimed, just foalting around to grab.
AKL is zero entry, has a nice slide a 2 year old might be able to handle (not mine, she won't go with out me.) It also has a great play ground. (and 2 hot tubs.) Both are really young child friendly resorts. One of my favorite things about AKL is you don't share busses with any other resort and there is just one stop. That really cuts down on the time you spend on the bus, even if you kind of far away from most of the parks (MK only).
Have a great trip. I like WDW in March, sometimes it is a bit busy, but not like a holiday or anything. (We have to go when Mr. PhD's school is on break.)