Hi Christine!
Thanks for stopping by the Disney Parks Moms Panel with your question - I'm happy to help.
While most average sized tote bags/purses/diaper bags/backpacks are allowed, Walt Disney World Resort asks guests not to bring suitcases, coolers or backpacks, with or without wheels, larger than 24" long x 15" wide x 18" high (61cm x 38cm x 46cm) into the theme parks.
All guests will go through a security check/bag inspection before entering any of Walt Disney World's four theme parks. Guests may also be asked to go through an additional screening area with a walk-through metal detector upon entry.
You can find more information about
Park Rules and Regulations on the Walt Disney World website.
I hope this helps with your planning! Have a magical day! - Diane W.