That is so heartbreaking. Good thing you came along. Since you got their license plate, authorities can definitely take action. You can also offer to identify the kids if the authorities are concerned about proof. It might have been a parent's vehicle, but you got a good look at the kids twice. And I agree that it is a scary warning sign of what is in these kid's hearts, and there is a good chance they will progress to even more violence if it's not addressed now.