With the situation being what it is, children should be on alert as soon as they can understand what it means. When I was a child in the 60s, we had duck and cover drills because of the possibility of a nuclear attack, and it was understood that our youth wouldn’t save us. School shooters have proven they won’t spare small children, either.
My cousin recently retired from teaching in the "inner city", and said, "our schools have been equipped with metal detectors and security guards for decades now because of gang activity. We haven’t had any school shootings comparable to Uvalde, Columbine or Newtown. It’s kinda saying something when schools in the "hood" are suddenly safer than in the suburbs." 🙁