What’s the correct plural possessive of “kids”?

I know that children’s books is correct, but for some reason I want to say kids books, even though I know that it’s a plural possessive noun ending in an s.

A quick search on the web turns up Barnes & Noble, who have a web page title that reads “Children's Books, Kids Books”.

Is the major bookseller wrong here? Or is there some exception I don’t remember?

More simply, is it kids books or kids’ books — and why?

Part of my answer to the question posted here was:

According to ‘The Cambridge Guide to English Usage’, the removal of the apostrophe from 'plural nouns in phrases which express affiliation . . . is widespread in the English-speaking world' and has the imprimatur of the American Associated Press stylebook and the Australian government Style Manual. As the Cambridge Guide says, ‘the time spent worrying about whether it should really be driver’s licence or drivers’ licence would be better used elsewhere.'

Nothing is lost by writing kids books rather than kids’ books. However, the Cambridge Guide does point out 'that there are special cases which seem anomalous without the apostrophe s', and one of them is childrens, 'because that is not a regular form of the word . . . Thus context is the final arbiter as to whether apostrophes are needed, as always.'

Either is acceptable.

Kids' is a genitive determiner. (Like our, the cat's, the man who stole my wallet's, and so on.)

Kids is a noun modifier. (Like machine in machine tools, book in book publisher and so on.)

The worst that could be said about the publisher is that it is being grammatically inconsistent. Mind you, for a book publisher, that's quite an indictment.

Aside: Often, when a noun is used as a noun modifier, it is forced into the singular form. For example, trousers is always plural, but the trouser in trouser press is singular. If this rule were strict, you could argue that the form using the noun modifier should be kid books rather than kids books, but exceptions like glasses case show that this rule is not strict. If somebody can explain why the rule is followed for trouser press and not glasses case then we may have a case against the publisher.

I think that the Barnes & Noble web page example is a useful illustration of the shift in usage that is occurring at present. However, it is also sadly inconsistent.

There is a general tendency to switch to the noun-modifier option when an attributive (in the sense of a construction denoting association) rather than a true possessive is intended (but not otherwise):

We bought the children's clothes at the Childrens Clothing department at Garrods.

Garrods can of course decide on whether they prefer an apostrophe or not.

Notice that we have disturbing new nouns (used solely as modifiers): childrens, mens, womens; writers guilds smugly don't need any.

To answer the question, the correct plural possessive of kids is kids’. It's a standard plural and takes s-apostrophe.