Interesting, helpful article from Patty from Hand in Hand Parenting. This one explores helpful/unhelpful responses in this emotionally demanding situation, to the child who has been hurt, to the aggressor and also looks at how the parent can best look after themselves (we are less likely to be able to respond usefully to either child, if we are tripping over our own emotion, e.g. distress and anger).
There are tons of other helpful resources on the Hand in Hand Parenting site, and the insights are relevant and useful in many contexts besides parenting.
Palace Gate Counselling Service, Exeter