This isn't to say that one must not defend against an attack
especially for your safety or the safety of another. Personal
defense based on the moment is not fostering a thought
pattern of attack.

Proper defense is the neutralization of attack.

Certainly the child bully is imbalanced and often their actions are
a reflection of something they have seen and heard. Perhaps the
situation is created by the bully being physically larger or
stronger than the other children.

The child bully most likely hasn't yet developed to a point where they
see their actions as socially improper and are not able to comprehend
the reasons not to repeat the actions. So talking to the minor child
is not the proper course.

Talking to the parents is the proper course, but not necessarily a solution.
In fact, the parents may react strongly or encourage the child to continue.

This is one time when you must use best judgment and reason
to find a common ground between all of the parents involved.

If this is on the grounds of a school the proper school personnel
should also be involved.