I have a 6 yo daughter and 3 yo son. Daughter is often "mean" to son verbally. His 3 yr old talkativeness bothers her, and she frequently shouts at him ("be quiet!" etc.) My and wife's approach has been to not get involved, as the shouting usually does not appear to affect him, and I don't want to make matters worse through the "vicious cycle" of perpetrator vs. victim that Rosemond writes about. On the occasion when son does react, and the two get into a mutual shouting match, we send both to their rooms.
The other day, son got into daughter's belongings, and daughter pushed son down. I sentenced daughter to her room for the rest of the day. I did not send son to his room. I am now rethinking this. Of course, hitting must be addressed firmly. But perhaps both should have been sent to their rooms, out of concern of the "vicious cycle." (After all, the daughter's 6 yo irrational mind surely thought that son's actions justified the push.) My wife and I have been faithful to Rosemond's advice to not punish according to who appears at fault (in the adult world). Do you recommend sticking to this principle, even in situation such as the one above?