Hi Kay,
  Ooh...I am SO excited for you! 
Mickey's Very Merry Christmas Party is my very 
favorite special event of the year! With shorter wait times for attractions, the chance to greet some rarely seen characters, snow on Main Street U.S.A., delicious complimentary treats, the spectacular Holiday Wishes fireworks show, and my very favorite, Mickey's Once Upon A Christmastime Parade, it's an evening FULL of magic! You're going to have a BLAST! 
 While the official event doesn't begin until 7:00 p.m., in the past they have allowed Guests with a valid Mickey's Very Merry Christmas Party ticket to enter as early as 4:00 p.m. Your 3:00 p.m. dining reservation will be too early to enter for the party, so you would need to use a day's regular ticket admission if you'd like to enter Magic Kingdom Park prior to 4:00 p.m. If you don't want to do that, I'd suggest trying to modify your 
dining reservation time for just a wee bit later in the day. 
 Thanks so much for visiting us at the Disney Parks Moms Panel, Kay, and please let us know if we can help with anything else! You're visiting at a really wonderful time of year where Christmas music and gorgeous, festive decorations bring the entire Walt Disney World Resort to life with holiday joy, and I hope that you'll be able to enjoy 
many of the 
special events. Have a truly magical vacation! 
 Missy