That's scary. Families are tough about those things sometimes. They don't want to admit something is terribly wrong. I am honestly not sure what to advise. At best the employer might view this as making work a hostile environment because you told him to stop and he didn't. That would be a start.
School or parents… try with whomever you feel more comfortable with. The school is going to document it and possibly report to the parents. Unless the girl came forward there is not much they can do. It is impossible to know how the parents will react unless you know them. Ideally you'd like to see them do something but a lot don't. . I wish I could offer more. You are in a really tough situation. It is really hard to know what to do. I commend you for asking for help.

If nobody helps appropriately or if he gets scarier you can report it to police. They may call the school and /or parents. I don't think they can do anything else but they take this sort of thing very seriously these days and if he did go further it would help to have some background.

Sent from my iPhone using Tapatalk