Hi Celeste,
What a great celebration for your son to come to Walt Disney World! And by coming in mid-December, you should be able to escape the heavy crowds of the week over the holidays.
First, the general weather can actually be quite varied in December. When we were there this year, we had a few days in shorts and other days in pants/jacket (average temp, by the way, is 62 degrees in December). I'd encourage you to follow the weather forecast prior to your arrival. I use www.weather.com and www.noaa.org.
You may be able to find some
Special Offers that are offered to all guests (nothing specifically like you listed, however), but nothing is available right now. If you work through a trusted travel agent (AAA often has agents that specialize in WDW travel), s/he should be able to help you locate special offers, too.
And finally, there are
wonderful holiday happenings at WDW; it is truly magical!
Have a wonderful trip; please let us know if we can help again.