Let kids know honestly how you feel about what happened. If you talk freely about your feelings, you're giving them permission to talk freely as well. Support your teen's feelings. If they seem indifferent, talk with them about how hard it is to cope with painful feelings. I feel awful for those students and their families.
Compassion is an essential quality in a well functioning human being.
Letting your kids see your strong feelings about the victims nurtures compassion. It also helps teens distinguish between the shootings and film or video violence. This is not likely to happen in your school. Kids need to be reassured that they are safe. In fact, this kind of violence is not likely to occur at most schools.