Christmas in Disney World is really special and if you have a chance to experience it I say go for it!
The weeks between Thanksgiving and Christmas Day are typically low attendance and perfect for a first time trip with little ones. You'll be able to see all of the magic that Disney puts in the Christmas decorations, but also experience the Parks in all their less crowded glory!
Another bonus to early December at Disney World is the weather; lower on humidity and a mild high temperature. The nights and early morning can be a wee bit nippy, but layers for you and the kids solve that.
The first couple of weeks in June will have more crowds than early December, with some websites ranking them at moderate levels and some at high levels for 2010. Those weeks have not, historically, been very high crowds. The highs are generally in the high 80's to low 90's.
Thank you for visiting with us here at Walt Disney World Moms Panel! I hope that you have a Magical trip!