I have been involved with the public school system for about six years and although I know the student handbook forbids weapons of any kind on school property, I don't recall ever hearing a discussion about it amongst the staff and students. Every grade level learns about bullies and how to deal with them, but are we teaching our young elementary students what to do if they suspect a fellow student has a weapon? Not that I can recall.
Hopefully, your kids are aware and will never have to face this issue, but it is worth discussing with them at home several times over the year. It is also worth bringing up to your school board. It can't hurt to expand the bully discussion just a little wider in the younger grades. Can it? Grab a latte, put up your feet, and join the discussion!