How much detention time could a 13 yr old get for domestic violence charge?

My son hit his sister in the face and her face was swollen, I called the police to teach him a lesson and they came and took him to juvenile and within 1 day, he was facing a criminal charge of domestic violence. He has never been in trouble before. He is going through depression and is angry about not being able to see his father. He just recently got expelled from public school for trying to sell a bb gun in school to another boy because he could not have it without me knowing and now is in current violation of his diversion probation. I am having a hard time finding a good therapist for him, I know something is wrong with him but I am having a hard time getting the help that he needs. any one knows the juvenile legal system and what I could expect? Also, what could I do to get him properly evaluated to help deal with his depression and anger? I really do believe something is wrong with him. How do I prove it? How do I get help? where can I take him to get him properly evaluated? He is really suffering eternally, and it is taking a mental toll on me. Any serious suggestions please.