How does a noncustodial parent gain custody of their children from an abuse custodial parent?

The father has had the children since 2009 . There have been multiple reports of abuse on the 5 children living with him. More recently, my 13 year old daughter (14 in June) was hit in the eye by her father, ran away to a nearby store and called the police. She had a black eye and a scratch. DCF was called, and they spoke to all of the children. The other four children told DCF that it was an accident and that he doesn't abuse them. DCF said I told her what to say. The children were left in his custody. I filed a restraining order on my daughters behalf. When he was served with the papers, DCF said she could not come with me. They sent her to her Grandmothers house and when we went back to court, they dropped it. Dcf ALWAYS says she's lying when they are called for anything she says.