You will find a section for childrens’ books, but no “adults only” section.
You may find a glass case for expensive books or books which are commonly vandalized (including explicit photo books where someone just wants to keep one page).
I’m not quite sure what the difference is between keeping the kids’ books in a specific section, which is what I see, and having an “adults’ only” section, like you’re talking about. Are you saying librarians need to check ids to let people browse the stacks? Let’s not argue about checking out materials because that’s a different matter, you’re refering to “sections” in the library.
And I think parents should supervise their children’s library access. If Mom scans through books BEFORE the kid goes to check them out, then we have nothing to throw fits about.