My son is about to turn 3yrs now and I also have a 1.2M old daughter..He always hits her badly... Trying hard to make him understand but of no use....for few minutes he will be fine with her and play and all of a sudden he starts hitting her....this behaviour is only with few members who are known to him .....but in school he behaves very normally....I am worried about him....the way he hits her is very dangerous....please guide....how to control him is this behaviour is normal