Hi Skyler,
My family spent Christmas and New Year at Walt Disney World last year and it was very cold. We needed winter coats, hat, scarves and gloves most days. That said, I think that this was unusually cold for that time of year. The average high temperature in Orlando during December is 73 degrees fahrenheit with an average low of 51 degrees fahrenheit.
My best advice to you when travelling at this time of year is to pack plenty of layers and that way you will be able to deal with all types of weather conditions.
Mickey's Very Merry Christmas Party is a special event held each winter on select nights at the Magic Kingdom theme park. This festive celebration is a lot of fun for all the family and includes Mickey's Once Upon A Christmastime Parade, Holiday Wishes fireworks extravaganza, the enchanting Castle Dream Lights, a magical snow fall on Main Street U.S.A. and much much more.
Purchase of an additional event admission ticket is required to attend Mickey's Very Merry Christmas Party. These can be bought ahead of time on the Walt Disney World website
HERE.
I hope that this information has been of help and wish you a magical trip!