changing custody?

My ex and I have been divorced for a year. We have been sperated for two years. During that two year period, she has moved my two small children from 3 different households and 2 different day cares. I also have reason to believe that she is not taking care of my children properly. I called CPS and she told them that I abused the children. After we went to court about that I have contiued my visitation. My children never want to go back to her.
My lawyer said that I would have to prove that she is doing something wrong, in order to gain custody of the children. I live in AL. My ex has sole custody of the children now. She also will not tell me where they are living presently. I do not have the proof that is necessary for changing custody. Would I have to have the same kind of "proof" of neglect or abuse if I just wanted to change from her having sole cusdody to us having joint custody?

You need proof.. but you could petition the courts for not knowing the location of the children and therefore not able to call them.