Answer: It depends on the circumstances. The first question is whether there is actually a sexual relationship. If there is not a sexual relationship going on, there may be no legal action for a parent to pursue. If there is a sexual relationship, the parent can consider filing for a restraining order on behalf of their child or in contacting the local police department to investigate. Depending on the facts of the case, these procedures can have different results. So consult with an attorney and be informed about the local practice before you take any action.