Wishing that people, old or young, should stop carrying knives is no good at all, although I understand the sentiment.
What is needed is a law making it illegal. It is actually illegal where I live to carry a knive unless you have a hunter's licence and are actually going hunting, a craftsman whose craft necessitates the use of knives and are at work or going or coming from work, a serviceman or woman in uniform or a boy scout or girl guide in uniform, or a licensed angler out fishing.
And, of course, the law needs to be enforced and punishment suitable. Carrying a knife illegally leads to a fine and confiscation of the knife the first time you are caught. If you do it more than once the fine is increased, or you may be sent to prison.
Inflicting grevious bodily harm, or killing someone is treated as these crimes always are, which means prison for at least 12 years for murder or culpable homicide, and only slightly less for manslaughter.
As youngsters are apparently bringing knives with them to school, both teachers and janitors need to be authorised to search school-bags before pupils are allowed into the school grounds. This would entail employing trained security officers to do the job, but if it saves lives the expense is justified.