Hi Laura!
How awesome to enjoy a Halloween and a Christmas event while on the same Walt Disney World vacation.
Both special events,
Mickey's Not-So-Scary Halloween Party and
Mickey's Very Merry Christmas Party, are great family experiences.
Guests with tickets for the party can access Magic Kingdom since 4:00 pm and the party starts at 7:00 pm. When the party begins, guests without ticket for the party are escorted out of the park.
Parades of both special events start at 8:15 and 10:30 pm. The first parade usually has larger crowds than the later.
During the second parade we have always find a great spot just before the parade starts.
Crowd level at these parties is usually low and during late hours these can be really low.
I highly recommend a midday break / nap on the days of these parties and a light itinerary on the day after.
Thank you for visiting and letting us help you plan a holiday vacation at Walt Disney World.
Miguel