Without addressing whether this problem is rampant where, we all agree that ANY such cases are too many. I want to just reinforce something that was mentioned by previous posters. The first line of defense against abuse, even from family members is to educate our children.
From a very young age kids should be taught that they NEVER need to keep a secret from those who care about them. If anyone does something to them or makes them do something and tells them not to tell anyone, they should immediately tell a parent or another adult that they trust. Even if they promised not to tell, or if the person told them they will get in trouble, or if the person telling them to keep a secret is a relative or teacher, they still MUST always tell someone else. Older kids can understand that if an adult or older child is doing something to/with them and insisting on secrecy, that is a sign that it is likely wrong.
And of course kids should be taught that their bodies belong to them, and no one is allowed to touch them in a way that makes them feel uncomfortable. Also no one may touch them, and they should not touch anyone else in any private part of the body, even if it does not bother them or feel bad, and if it happens they should make sure to tell an adult they trust right away.
Molesters depend on the secrecy of their victims. Empowering children to break that secrecy in the very early stages of an abusive relationship is one of the main preventative actions we can take.