C.J.
Since you have to stick with what you already told them, and since "Santa sees all"......if they realize things on Christmas morning you tell them "Santa saw how much you liked the books I bought for those little boys, he brought you the same ones!"
Because my kids have free roam of my entire house, I keep everything at my mom's house. She brings it over late Christmas Eve. Otherwise there would be no way I could get away with hiding stuff!