Normally one incident is a smoke screen for something else, perhaps abandoment already experienced by that age, perhaps your brothers sense of responsibitly for you was an example of him having to take over the parents role? I remember being taken to sch with my brother when I was 5 accept he would hit me and run from me,that was just how our relationship was, the damage wasnt from one incident, the damage was spotlighted by incidents, if you get my drift.