No question..3 nights at CSR with one day each at your two parks of choice. Two nights with a day of travel on each side might be a little too much of a whirlwind for your little ones. I think three nights would give everyone a little bit more time to enjoy their experience. While I love the Poly, and it is a gorgeous resort - fun, wonderfully themed, great rooms, IMO, it is something you can experience by having a meal or seeing the show at the resort. Unless it is your dream to stay at the Poly and this will be your only chance to stay at the resort my vote would be for the extra day and night at CSR over the Poly.