Scooby Doo Backpack - Medium Size Mr Machine And Scooby Doo Backpack . $15.88. Makes a great gift. Medium / Toddler Sized Backpacks are recommended for Kindergarten age or younger. Medium / Toddler Sized can hold an 8.5" x 11" standard sized folder. If your child has to carry books to school please order a Full Sized model.