How is your son doing? Is he fearful of dogs now?
I think you have to just do what you feel is right, there is no "right" answer in this situation. On one hand you put down a young puppy and protect others from future bites, and on the other hand you re-home them in hopes that they are properly trained and this doesn't happen again, but there is no guarantee. It's a lose-lose situation. It's great that the owners are being so responsible. On a side note, have you seen how they train their dogs? That might offer some insight as to why they behaved the way they did.
So sorry for this situation and good luck
