Will my child or the caller know if I block a number from their phone?

Without making too many details…..My child is in communication with another, "cool" child, who is talking her into doing….less than savory or legal things. I know there's only so much I can do, but I'd like to block this other child's number using the Family Allowances, as I have very nearly had it at this point. 

I'm afraid of there being a blow-up if she receives some kind of notification that a number has been blocked. I would rather she just not know, and for the person calling/texting to also not know. Even if it's only a temporary fix, allow them to think that one has ghosted the other. 

If I block this number from this phone, is that it? I know it sounds silly, but I'm paranoid since I don't want any more of this drama. There's been enough of it already.