TATL (pronounced tattle)
T - Talk to your child. Ask them about what happened.
A - Authorities. Don't go to the principal. Don't go to the head coach. Go to the police. They are trained to deal with sexual predators and are very compassionate.
T - Therapy. It will be the best investment you make toward your child's betterment.
L - Love your child. Let them know they did nothing wrong. Tell them it wasn't their fault and that you are there for them.