What can the parents be charged with? Clearly the dog was a known danger and they were extremely negligent.
We were taught in law school that under the English Common Law, “every dog is entitled to one bite.” That old presumption flies in the face of this new American breed which started in the middle 19th century. Some jurisdictions simply ban the Pit Bull. I would suggest a rebuttable presumption of reckless endangerment (gross misdemeanor) in any biting case with such animals. Or a more severe presumption against the dog’s master, such as intent.
And killing such dogs is imperative.