We are going Jan 6-13th!! Our first family trip to Disney

We are giving this trip to the kids as a Christmas gift. They will be so excited. They are 7, 5, and 6 mos. I really want to tell them but the looks on their faces will be priceless on Christmas morning. We figured we would go while the baby was small, thinking it would be easier. Hope it is. Does anyone know what the weather is like in Jan?