The Fastpass system allows you to avoid long lines by giving you the option of coming back to a ride or attraction at a later time for a shorter wait. Just insert your admission ticket or Key to the World card at the Fastpass both and it will give you a ticket with a time on it for when you can come back to ride the ride. You can use the Fastpass at any point after the return time but not prior. You cannot obtain another Fastpass until after the return time on the ticket or two hours later, whichever comes first.
If you decide to stay on the property at any one of the Disney World resorts, you will have the option of taking advantage of Extra Magic Hours, which are extended park hours for guests staying on the property. This allows you to have an extra hour before and after the park closes to take advantage of rides and attractions with short wait times and less crowding. Having extra hours also allows you to take a break during the day to recuperate without losing precious park hours.
The best way to get the most out of Walt Disney World is with a Park Hopper Pass. This ticket gives you access to all of the Disney parks at once, allowing you to have better plan your trip. Some parks, such as Animal Kingdom, don't have much to do in the evening hours while other parks like MGM Studios are better at night. With a Park Hopper Pass you have the flexibility to go with the flow instead of planning for one park per day, so you have the ability to go back and see what you missed or end a day in one park early so you can get a head start on the next.
If you are traveling with little ones you need to ensure they don't become fatigued throughout the day by taking plenty of breaks for water and shade. You may even need to take time each day to go back to the hotel for a quick nap or down time at the pool. Bring sunscreen and talcum powder in travel bottles to prevent sunburn and chaffing. Before visiting the park, check that everyone in your group has a pair of comfortable walking shoes, that have been broken in, and clean dry socks to avoid blisters.