The question arises because of reading that a famous music artist had hushed up instances of sex with a minor through the use of non-disclosure agreements. Making these enforceable in a civil setting would seem contrary to the public interest in having sanctions fall solely on the adult in such an instance.
I suppose a further question would arise whether non-disclosure agreements regarding any illegal acts would be enforceable, but I imagine the such agreements might sometimes be evidence of violating laws regarding conspiracy to obstruct justice. (I'm not a lawyer, so accept any mangling of proper terminology.)
So I guess the overarching question is what sort of statutory or common law restrictions exist on the enforceablity of non-disclosure agreements? I do understand that practically the mechanism may be more "effective", even in the absence of enforceability, due to unwillingness of victims or witnesses to provide evidence.