Hi Jessica,
Welcome to the Disney Parks Moms Panel! It looks like you'll be arriving at Walt Disney World in just a few short days, and I know just how excited you are!
My Padawans have learned the ways of the Force at
Jedi Training: Trials of the Temple, and it's always such a fun experience. From the moment your youngling slips into the Jedi robe, they will feel at one with the Force, and I know they will love every minute of their training experience.
Jessica, Jedi Training sign-ups begin at park opening, not at the start time of
Early Morning Magic, which is focused on Toy Story Land attractions. However, you're right that Guests are sometimes let into the parks a little early (for example, they may start moving Guests down Hollywood Boulevard at around 8:40 a.m. on a 9:00 a.m. opening day).
It sounds like you're planning a day of park hopping, so that will impact your strategy. In my experience, the morning slots go quickly, and most slots are usually gone within an hour of park opening. If you can be flexible with the time, I would choose Early Morning Magic, because it's such a great opportunity to experience
Toy Story Land with minimal waits.
Definitely talk to a Cast Member when you arrive at Disney's Hollywood Studios to see what they advise. Their protocols change all the time based on crowd levels, and they will have the best advice that will help you make the most of your time.
Sending lots of pixie dust for your magical marathon day of Walt Disney World fun!
May the force be with you, and have a magical vacation,
Robyn