The 'verbal argument' aspect of the reporting is concerning me. We don't yet know what happened of course, but the language seems potentially victim-blaming. It could be the case of a group of boys harassing a group of girls and then getting angry when the girls talk back.
Knife amnesties aren't necessarily a bad idea but ultimately they are a PR exercise. The real problem is that there are a significant number or people, mainly young men, out there who actually enjoy being intimidating, who actually enjoy violence, and who have the mindset where killing someone over nothing is a normal thing to do. I don't know what the answers are but, while we need to do all we can to prevent parents and society from raising children this way, once someone becomes a criminal the punishment needs to reflect the weight of the crime. There are lots of people from deprived or abusive backgrounds whose experiences make them kinder and more empathetic adults.