When children are young, young enough to understand even the littlest things, parents often tell them: don't talk, take candy, or go anywhere, with strangers. Children know what it is like to get hurt by someone else, whether by a sibling in a fight, fights at day care and primary school. The parents tell them how wrong it is for them to hurt, based on how they would feel if they were hurt. So pain and danger is breached to children for their safety as early as they can understand it. They are taught the dangers of the world around them, since no matter how often a parent can try, they cannot always be near their child to keep them out of danger, whether from themselves or others.
Also, when a child is old enough to start asking why about everything, what does a parent tell them when they ask why are they eating meat, why are they eating other animals, why are they eating plants. What would a parent say? It, I think, it is difficult to tell children, despite what the socio-mind programming has taught us about our 'place' in the food chain on Earth, that we are not at the top of the food chain. We are predators and herbivores, and just like herbivores, we are prey to other predators. Why does the dog chase after the cat? Why does the cat drop off the mouse on the porch? In addition to using nursery rhymes, fairy tales, and the similar, we can also use the real world, in young enough terms, to get across the point that we too are food for something else, just as something else is food to us.
Maybe even better, most kids at some point in their young lives, start hollering because of a monster in the closet, under the bed, etc. Maybe this would be a great time to sit down with them, calming them down and explaining that yes there are monsters that exist, that there are reasons to be wary, not scared. With just acknowledging the existence of creature they already think exists, the parent can start teaching their child, giving them the knowledge about monsters, for their own protection; so that if the child sees, or feels that he/she sees, a monster they can call for their parents, they can react with their knowledge that the parents taught them to protect themselves. Knowledge is protection.