If the dam (mom) is a purebred American Shorthair with papers, and the sire (dad) is a purebred American Shorthair with papers, then all the kitties will be purebred American Shorthair.
If the sire is not purebred, NONE of the kittens will be American Shorthair pedigree.
Just so you know, the term "American Shorthair" is the name of a particular breed, like Siamese or Abysinnian or Burmese. It's not just a description of the color of the fur or the length. When a person states that their pet is a particular purebred breed it usually means that at least 4 generations back it has purebred lineage, with registration papers etc.
Are you confused with the term Domestic Shorthair (which means that it is a "regular" cat, the kind that are found in many neighborhoods and animal shelters)? So your question is if dad is a Domestic Shorthair, and mom is Domestic Shorthair, will kits be all shorthair?