Welcome to the Disney Parks Moms Panel, Denise!
I'm happy to help get ready for your trip to Walt Disney World Resort!
Parking at the theme parks includes exit and re-entry to any of the four theme parks on that same day. So once you pay for parking once, you can leave the theme park's lot and show your parking ticket to the Cast Member to park again at that theme park or a different park. This has worked out great for my family if we need to leave to take my kids back to the hotel for a nap or to take a trip to Disney Springs!
Guests two years old and under do not need a ticket for the Walt Disney World Resort theme parks. While you may be asked your grandson's age when you enter the theme park, you will not need to bring identification for him. In my experience, my boys love to scan their MagicBands, even though they don't have tickets, so they can be just like the big kids!
Please let us know if you have any other questions as you prepare for your trip! T-T-F-N, ta ta for now!
~Crystal B.