I have not stayed at the YC, but we have stayed many times at both the Poly and the BC. While we love the YC/BC pool, it is a really big area. It works out great when we are traveling with a large group, and the kids can stay together, but with just you and your son, I would choose the Poly. It has a great pool area, and since it is smaller, the kids always find others to play with so you can relax and still keep an eye on him. I would also mention that even though my son is a pretty strong swimmer, the lazy river at the YC is very deep (maybe 7 or 8 feet) and makes me nervous if he is on his own. That said, I would pick the Poly over anywhere else just for the location and grounds. I love the relaxed feel of the resort as well as the prime location on the monorail.