Hi Kelly,
Exciting indeed!
Mickey's Very Merry Christmas Party is one of my fave events at Walt Disney World. And you'll have the opportunity for numerous photo ops that would make excellent Christmas cards!
When you enter the Magic Kingdom, pick up a party map. It will list all of the amazing character greeting locations.
While character greetings are subject to change, you can pretty much count on Santa, Mickey, and Minnie being in attendance.
Last year, Santa was near the Town Square flag pole, while Mickey and Minnie dressed in their holiday attire greeted guests from the Town Square Theater.
There's usually other fabulous photo ops such as all seven dwarfs near the exit to Splash Mountain.
Lines can become long for the characters so try to accomplish this upon arrival. Enjoy a memorable party with your family!