Hi Helen,
Welcome to the Disney Parks Moms Panel! Hooray for first visits!
My heart is torn on this question. On our girls' first visit when they were 5-years old, they needed to rest in the afternoons. We also limited ourselves to certain areas of the parks. There was no way we could do everything. So, my instinct tells me that you should take it slow and focus on three parks. But, then we have to choose which parks and that is tough! The other challenge you would have with visiting more than one park per day would be that you can only make your first three initial
Fast Pass+ selections at one park. If you plan to visit Magic Kingdom in the morning and make your Fast Pass+ selections there and then visit Disney's Animal Kingdom in the afternoon, you would only be able to make Fast Pass+ selections for Disney's Animal Kingdom after you have completed those first three Fast Pass+ selections or the ride time windows have expired.
With that dilemma in mind and given the age of your son, I suggest that you stick to three parks. With Toy Story Land and Jedi Training - Trials of the Temple at Disney's Hollywood Studios, I would say that park is a must-do. Choose Slinky Dog Dash and Star Tours - The Adventures Continue for your Fast Pass+. Check the height requirement for Avatar Flight of Passage at Disney's Animal Kingdom. It is a must-do Fast Pass+ selection if you pick that park, but he may not be quite tall enough yet. If you go to Epcot, do Fast Pass+ with Test Track and Mission: SPACE. Once again, check all of the height requirements. Soarin' Around the World is also another option if you choose not to Fast Pass+ Test Track. At Magic Kingdom, do Seven Dwarfs Mine Train, Big Thunder Mountain Railroad and Splash Mountain. Make those Fast Pass+ selections - availability is limited!
Magic, memories and Minnie Mouse hugs,
Donyell