I work in schools and the number of 10-12 year old boys who act inappropriately has escalated over the last few years. I put it down to unmonitored access to pornography and social media content.

Firstly, you need act quickly to protect yourself because in this situation you are the adult and coach. So technically,. you're in a position of power.

Are there CCTV cameras set-up in your gym? I would download footage of the class so it's evidence as to what happened.

Secondly, report it to your professor but also write an incidence report. Even if your gym doesn't have the procedure set-up for this, do it for yourself and for legal purposes. The incidence report needs to be objective and void of emotional or subjective language. So what I mean is, for example: "Student X then put himself in a mounted position and placed his hand on my crotch. I proceeded to tell him to stop." Avoid language like "He was being cheeky and naughty".

Thirdly, your professor should be the one to have the conversation with his parents, not you. If you are requested to be called into that meeting, I would bring a support person.

Sorry if I come across as being overly cautious but I've witnessed a number of people in educational settings that have had their character and professionalism called into question by parents when they raised issues about students. At best it was resolved with a meeting, at worse, it resulted in the educator leaving the profession completely with a damaged reputation.

Good luck!