Yes, because they're the responsible adult, by virtue of their job and you'd hope their age and experience, and its their actions that allow it to become a possible risk. Children of course should be taught properly, but they're also impulsive and not wise and lack education, so we don't treat them as responsible for their actions (with caveats) in the same way we do adults.

Small children can have older siblings or friends who might show them that, and sometimes parents aren't responsible or good parents, sometimes children themselves are innapropriate because of harmful upbringing - this might be unusual or unlikely, but with children (and an institution entrusted to care for people's children) any small risk must be treated very seriously.