I have 2 children with a man that I've never been ...

I have 2 children with a man that I've never been married to and I caught him buying drugs in front of our 2 very small chilren and haven't been with him after that for 7 or 8 years now. This man is a drug abuser "meth being his drug of choice", and he can't keep a job for very long, but he has to because he has to pay child support. He has always told people lies about me and now he's telling people that a bug bite that my child got while he was at his house is a cigarette burn and he's telling everyone my brother burnt my child with a cigarette. My brother whom I rarely see doesn't even smoke! He had a Doctor go along with his story and the reason she went along with his story is because I was homeschooling my children at that time and she doesn't like parents who choose to homeschool their children. How can I prove my innocence? The burden should be on them, but I'm told that it is my burden to prove that I am innocent.  If it was a burn (which it was clearly a very small mosquito bite that my child had scratched) then wouldn't they have to prove that it had actually happened while he was in my care. I have so much evidence against this guy, about how violent he is and how very mentally unstable he is. I have medical records showing that he broke my leg in 3 places and it states that the "boyfriend" did it. He just got out of a mental stablization center, but they won't use any of that. Does something seem like a set up to you? If anyone can help me with this matter I would appreciate it very much.