I have to agree with Shih-Tzu. Giving the dog back to the breeder is not the answer. A dog begins certain behaviors for a legitimate reason (the same way a child after being potty-trained for over 2 years begins to wet his bed). The same way you would not give up on finding a way to help your child stop wetting his bad, you need to find the problem as to why your dog has begun biting. It is not impossible to do this. You can go to just about any PetSmart or Petco and ask a trainer there for their suggestions/help and if financial circumstances allow, you can sign the dog up for a "refresher" course on things that are and are not allowed.
One thing that Shih-Tzu did not mention is the emotional problems that will come along with getting rid of your dog. It's more than likely your son has an attachment to the dog and giving him away will traumatize him and it will be something that will forever affect him. In essence, you are teaching your son that instead of trying to fix a problem, it's easier to give up and get rid of the problem. I am sure this is not your intention but this is what will be understood, consciously and subconsciously.
If you need any help in finding a local trainer or any other type of help for the dog, please do not hesitate to contact me. I will do whatever I can to help the situation so that your son does not have to know the trauma that will result from tearing away his pet.