> Does this imply that parents, or those delegated by them, would be commiting a crime by showing their children material out of the government's chosen age range? That strikes me as absurd.
Technically, yeah. And on the face of it, that doesn't sounds great does it? But again, that ignores the reality of the NZ justice system. I wouldn't think any parent has ever been prosecuted for that sort of thing. There are many safety valves like police discretion, prosecutor discretion, judicial discretion. If it got to court my assumption is that the offender would be discharged without conviction [1]. Basically given a telling off by the judge.
Any cases of a parent, or anyone just guilty of showing restricted stuff to a child, that resulted in fines or jail time would include large scale offending (distribution for profit probably), or some other abuse. I could certainly see a parent that was showing porn to their kid, as part of the sexual assault of that kid, getting a conviction for this, but only as part of a larger case involving a bunch of yuck stuff I don't want to think about.
Without doing a bunch of research, the other circumstance I could picture a parent being convicted would be in the dark times of the past. It wouldn't surprise me much to read that Mrs. Poorlady of Mangakino was convicted of supplying a minor restricted material in 1962 and fined £100. But all countries have weird pasts, McCarthyism was a thing.
TV and Radio aren't "publications" for the purposes of the Act. That is up to the Broadcasting Standards Authority. See: https://www.classificationoffice.govt.nz/classification-info... and https://www.bsa.govt.nz/
And lastly: yes a library would check your id. Libraries do stock DVDs and will absolutely not hand R16 movies to 15 year olds. But it is rare for books to get ratings.
Books are assumed to be ok, and most go unclassified. But books might be submitted for classification if the publisher thinks it is borderline. Or if a member of the public submitted it.
So yeah, if a book was submitted for classification, and that book got a restricted label, and the library thought the book wasn't trash and was worth stocking, then yes, they would check id if you look like you could be under the restricted age.
[1]: https://www.willislegal.co.nz/discharge-without-conviction/