Hi Claudia,
I can't think of a better place to spend Halloween than Mickey's Not-So-Scary Halloween Party at the Magic Kingdom.
If you want to spend the whole day at the Magic Kingdom you will need two different tickets - a regular ticket and a ticket to MNSSHP. A regular theme park admission ticket is required to enter the park any time during regular park hours that day (9:00 a.m. - 7:00 p.m.)
MNSSHP begins at 7:00 p.m. and lasts until midnight. It requires a separate special event ticket to attend and only those Guests with the special event ticket are allowed to enter or remain in the park when the party begins. Once party goers enter the park, they are given a special wrist band which indicates they have tickets to this event. Cast Members will be stationed at the entrances to the different themed lands. Guests who aren't wearing wrist bands for the event that evening will be asked to make their way down Main Street to exit the park. If you are already in the park, you will need to go back to the front to get your wrist band. OH! And your Trick or Treat bag for your candy - wouldn't want miss out on that!
If you are going to be in the Magic Kingdom all day, I'd suggest doing all the attractions and rides during the day and then concentrating on the special events for MNSSHP during the evening.
I hope you have a SPOOKTACULAR time! Wishing you many magical memories :-) Allison