The only thing we know without a proof is that they might be doing it. We don’t have a proof they do it but we also don’t have any proof they are incapable of doing so. A reasonable course of action would be to take precautions against it while not condemning them either, until they are either proven actually guilty or actively unwilling to up their security, which would also strongly imply the former.
You cannot let or forbid a 16yo to use stuff. You can only decide whether they will do it in the open or in hiding. Personally I’d rather have them talk to me about it than hide it from me.