If your kids are a little older and can stay up later, visit the Magic Kingdom in the morning when the park will be open late. In the morning, visit attractions with limited hours, see a parade, use all your Fast Passes, etc. When crowds peak mid-day, leave to visit another park, swim, or rest up. Return later, around 9 pm, and more often than not, you'll feel you have the ENTIRE Magic Kingdom to yourselves! Families with little ones are calling it a night by that time in the evening.