I get the strong implication that you killed them. You witnessed such cruelty, such extreme abuse and narcissism, that something snapped in you that night. You needed to show them all retribution, but your mind couldn't accept it and so made up the story about the doll coming to life, in your minds eye. "The sledgehammer was never found". "The dummy was still sitting in the chair. There was nothing alive about it at all". Did they lock you up I wonder? What did the police go with in the end? You were the only person there after all, and Lucy's mother was dead already.