Why didn’t the other children or the father support the child in the narrative, "A Child Called It"?

There are numerous adults in this memoir who know what Dave is going through, and yet do nothing to stop it. Dave's father looks on as his wife abuses his son, too weak to intervene. Dave's schoolteachers see his bruises and his malnourishment, but it takes them years to call the police. Over and over again, the adults in Dave's life refuse to do anything to help him, which is the primary reason Dave's abuse lasted so long. This is called the Bystander Effect".