回复：我该不该担心？

Above advice are sensible, and let me add some more:
1. Teach your child about body-safety: Do not allow anyone else to touch/see her private parts, not EVER.
2. Bring your concerns to the authority (that's the principal or director). Emphasize that you do not intend to cause any trouble with that male teacher, but you do have concerns--then tell her/him exactly what you wrote in your first post, if you could remember the dates, time, location, the names of the people present etc. to the principal. Remember, it's very reasonable for parents to have those concerns (I would if I am in your shoes) and it's very reasonable to let the authority know about your concerns. The purpose of talking to the principal is to have some assurance about your child's safety.
Good luck.