If your son is 12, and he made unauthorized purchases on your card, you should just pay those charges. It sounds as if you want to have it both ways, by claiming fraud to avoid payment of the charges, but then protecting our son as the alleged perpetrator. Just take responsibility as parent by paying the charges and learning to discipline and control your son better in the future. It would be better for you to teach him to be responsible for his actions, and the best way to do that would be for you to model responsible behavior yourself.
I am not your lawyer. Although I am a lawyer, here I am only giving general advice, based on the limited statement you have made here. You are advised to hire a lawyer, and get more specific advice tailored to your unique situation, if you have an important legal issue.
It’s not likely that you will get the charges “reversed” but if you get a good attorney, well versed in juvenile law, he or she may be able to get it resolved without a record. It’s certainly worth a try. Whenever I have young people as clients, or even adults with no criminal record, we do everything that we can to resolve the matter without a record, or at a minimum, without a conviction. It is not easy to accomplish once charges have been brought, but it is not impossible. It’s even more unlikely to happen without a good lawyer.