Hi Christi,
Thanks so much for visiting the Disney Parks Moms Panel with your question. I have attended
Mickey's Very Merry Christmas Party, and I have to tell you, it is a wonderful time. You will have so much fun with your boys!
As to what to expect at the party, you will find many attractions to be open, as well as special holiday entertainment and offerings including shows and dance parties. My biggest suggestion when attending the party is to be sure to take advantage of the entertainment and experiences that are not always available during regular theme park hours. Sure, it is fun to ride attractions at night, but there are experiences unique to the party that I think you should be sure to see. Two of my favorites are Mickey's Once Upon a Christmastime Parade and Holiday Wishes: Celebrate the Spirit of the Season. The parade and fireworks are so special for this time of year. In addition, I love having cookies and hot chocolate and watching it "snow" on Main Street, U.S.A.! Please do know that all offerings are subject to change.
Since you mention that your boys are little, and the party runs late, you might consider having some downtime during the day of the party. I would suggest a rest at your resort during the day so that they are ready to stay up late to experience all of the magic of Christmas at Magic Kingdom Park!
I hope that these thoughts are helpful for you, Christi. Have a great time planning your trip, and please do not hesitate to ask if you have any further questions.