They are brainwashed anyway, one way or another.
The truth and fact is that no one can say for sure what would happen after death. It's no wrong to get them prepared rather than to swallow a false delusion introduced by our secular education system. Inside this system, children are brainwashed to believe (with faith) that nothing will happen after death (a secular concept introduced by our education system without one's own consent).
I don't remember any education system that is secular ever teaching students that nothing happens after death. In fact, the topic I don't think has ever been brought up. Unless it's a college-level course in ethics, philosophy, critical thinking, or theology. That's not for children, however.
I know when one of my kids lost a friend in his classroom, and after a family member died the same year, he was able to discuss his feelings with the social worker and a couple of teachers and aides at his school. They offered him books on grief and remembering loved ones. But what happens after death was never discussed. They never even brought it up with me when I was informed that they were meeting with him.