Hi Kristina,
Thanks so much for visiting the Disney Parks Moms Panel with your questions!
There is so much to do at Walt Disney World. You could truly spend multiple days at each of the theme parks and still not do everything. My family has been vacationing at Walt Disney World for years, and there is still something new to explore and do each time.
I have a suggestion for you to go to the Magic Kingdom on two days and still be able to experience each of the other theme parks. Since you want to go to
Mickey's No-So-Scary Halloween Party, this is possible. Mickey's Not-So-Scary Halloween party is an event for which you need a separate ticket - you do not use a day of theme park tickets for it. I suggest that you plan your Magic Kingdom full theme park day for a day that is not the day you go to Mickey's Not-So-Scary Halloween Party. Plan your Mickey's Not-So-Scary Halloween Party for a day that you are going to one of the other theme parks - maybe for the day that you are going to Disney's Animal Kingdom early in the day. Then, that evening, head to Magic Kingdom for the party. Mickey's Not-So-Scary Halloween Party is so much fun for so many reasons, including trick-or-treating at the Magic Kingdom and special entertainment. In addition, many of the most popular attractions, such as Big Thunder Mountain Railroad and Dumbo the Flying Elephant, remain open during the party, so you can experience those attractions during the party with shorter lines.
I hope that this suggestion is helpful for you, Kristina! Please do not hesitate to ask if you have any further questions.