I,personally,am reluctant to classify any 6 year old as "dangerous".Yes,kids that age can do dangerous things and yes,these kids very probably need to be watched closely.
I'd bet everything I own that there's a reason for this that points to one or more adults....either abuse or having somehow seen a sick movie.
Six year-olds can be extremely dangerous. Children who are abused can exhibit psychopathic behaviors even at that age. I worked with a child who was around that age. I had a large fish tank—fish tanks generally calm people. Anyway, as I was a few feet away from “Jimmy,” he reached into the tank and retrieved a small crab, held it up for a second, dropped it and crushed it under his foot. Looking at me with the eyes of a dead fish, he announced, completely without affect, “the crab is dead.” By the time he was a teen, he progressed from torturing and killing animals to sexual predation. Not one of his numerous therapists or doctors would diagnose him as a psychopath because he was “too young.”
You’ll probably hear his real name on TV after he is caught for horrific crimes, but we truly have no systemic answer on how to deal with such children. This problem is much more widespread than most people know. The stories only hit the press for a few days and are usurped by the next Stormy Daniels. Abnormal psychology is so aberrant that most people cannot imagine it, much less understand. That desire to understand is in itself a large part of the problem. We don’t need to understand these people; we need to recognize them and take protective action.
“Barbarian” cultures are often criticized for their excessive punishments, but many could teach us a few things about protecting society. Our system not only allows these behaviors, it enables the perpetrators to progress to larger crimes. The question isn’t whether you’d incarcerate or kill a young Dahmer; it’s why not?