If you have children/grandchildren, I think you should talk to them about these school shootings & help alleviate any fears they have by talking about them. Remind them that school shootings are rare & if they hear another kid say something scary about guns/knives, they will be doing the right thing by telling a teacher immediately. Reiterate to them how important it is to do the right thing.
Remind them to pay attention & ask questions if they have any when practicing "active shooter" drills while at school.
We are having this conversation as a family this weekend & you may want to consider doing the same. It's a perfect time to remind them how much you love them & how important it is to speak up if they hear anything that worries them.