Hi Liz,
If you are planning to attend
Mickey's Not-So-Scary Halloween Party, and I highly recommend you do, you only need to purchase the party ticket. The official entry time on your party ticket is 7 PM but you can enter the Magic Kingdom Park as early as 4 PM. The web page has a lot of information, including a
Trick or Treat Map so you can be sure you leave with some goodies.
Be sure you make the time to watch
Mickey's Boo-to-You Halloween Parade. I think it's the best parade at Walt Disney World! The early parade is typically very busy. If your daughter can stay up late, I suggest trying to view the later parade. The later parade is usually a little bit less crowded.
Thank you for visiting us at the Disney Parks Moms Panel. Be sure to let me know if I can help you with any other questions!
Wishing you a magical, not-so-scary vacation,
Amy H