First off, this thread is about children fighting other children. There will be another thread started about children verses adult attackers.
I try to ignor what the parents have already tried to teach their child about self-defense. If they were experts, they would not be bringing them to me.
I teach them how arguments can lead to fighting. I tell them that VSD must be learned and practiced constantly such as kata is.
My students get this talk from me in front of their parents at the end of the class while they are kneeling down in the cerimonial bow... I ask "Why are we learning karate?" they raise their hands. I pick one of the newest students and he/she ususually replies "To learn how to fight". I say "No, we are learning how to defend ourselves from a threat of injury upon us from someone who will try to cause us physical harm". Then I say, "Is an argument a threat of physical harm? Yes. If allowed to continue without trying to stop it, it will lead to a fight."
By hearing from their Sensei that they are allowed to defend with verbal skills, they will not be so eager to strike the other child.
Scenarios can be a very good learning tool for children. Children will repeat what they are shown. Children will argue with each other over anything. One argument between children that will often lead to violence is when one is confronted because he/she told an authority person that the confronter did something wrong. Squeeling so they say.
Get two students to come up in front of the class. Tell one student that the other told his/her parents that they did not do their homework assignment, and the parents grounded the student for a week causing him/her to miss a social event that they very much wanted to attend. I also tell the student that in no way will they let the other talk their way out of a fight, and to attack the other student when I give them a verbal signal. I tell the other student that he/she has told on the student and that they MUST try to talk their way out of a fight. Then they begin to act out the confrontation. First I let them go at it alone and try not to interfere. I take mental notes about their posture and stances and listen to what they say to each other. It is very interesting to hear what they say to each other and most of them come up with a very good argument. Then the squeeled on student attacks on my verbal command, and the other must defend. I let them fight for about a minute to see what the defender will try to do. We talk about what happenend and how the VSD did not work and what could we say otherwise that might make it work.
It is very important to teach them that they must be on guard all the time while arguing, and that VSD will not always work in every situation, but they must try this first.
We then repeat the scenario with two more students (BTW at this point they all raise their hands and want to be the arguers) and try to make VSD work by saying other things that we talked about. This time we make it work and there is no fight.
Be careful when using these scenarios. The children will want to be in the scenario that leads to a fight. Make them understand that the no fight scenario is the desired outcome.