Beckton's son was reading from Stephen Chbosky's celebrated novel, The Perks of Being a Wallflower, a book bought on advice from a bookstore assistant. The blurb and cover had given no hint of the issues of drugs and sexuality it raised.

While the question proved a valuable opportunity for one of those mother-son chats, Beckton later told a conference of Australian academics that it was one she would have preferred to have when her son was older.

As a parent and a tutor at Central Queensland University, Beckton has been tracking the changes to young adult fiction, the growing sophistication of its content and its varied themes, and the way the lines between adult and teenager reading matter have blurred.

In her soon-to-be submitted thesis on the topic, Beckton questions whether publishers should do more to red-flag explicit content on their back covers or continue to self-regulate. Beckton makes clear she is not about censorship.

"As a mother, I want my teenage children to have unlimited access to a wide range of literature and that includes contemporary novels with controversial ideas and themes - there are so many new and fabulous books for teens to read nowadays.

"I also want them to be able to make informed decisions about what they choose rather than have those decision blurred by clever marketing techniques that are designed for maximum sales rather than reader need."

It was J.K. Rowlings' Harry Potter series that demonstrated the modern blockbuster sales potential of a children's book series with crossover appeal. Hollywood has since built multimillion-dollar film franchises from adaptions of Twilight, The Hunger Games and Divergent.

Beckton says many book covers in young adult fiction are age-ambiguous and offer little clue to the explicit nature of the content. She knows of one high school that restricts all such fiction to year 8 students. Even sales catalogues distributed through primary schools often show young adult books next to picture books, Beckton says.

Will Kostakis is author of the The First Third, a novel about a 17-year-old boy who helps his best friend Sticks come to grips with his awakening sexuality as a gay teen while his friend helps him work through his grandmother's bucket list.

The coupling is more implied than stated and related in the third person, says Kostakis, to give it distance. The age of Billy points to the book's targeted readership.

Last month, The First Third received the Gold Inky for best Australian book, as voted by teen readers.

Kostakis is not a fan of content warnings, saying they might mislead and deny teen boys going through the same sexual confusion a safe avenue to seek information about their sexuality.

"It's one thing to say there is sex and drugs in a book, it's another to say the context in which they are written. It's not as if the scene is glamorised. If you have a character going through a harrowing experience, that saves the reader from going down the same path."

Fiona Wood, who won Children's Book Council of Australia's Book of the Year (Older Readers) for her coming-of-age novel Wildlife, says the job of a writer is to serve the story, with honesty and integrity. The age of characters should be sufficient guide for readers.

"The novel is an art form, not a manual, not a text book. Where sex, or alcohol or drug use is represented, the way in which it is approached will ideally be motivated by story, and integral to character. It won't be gratuitous," she says.

"Of course you are also aware of your readers' ages, and the greatest respect you can give your reader is not to gloss over things you know that teenagers may encounter in their own lives."

Beckton says Margo Lanagan's award-winning book Tender Morsels has a note at the front of the publication that identifies some of its more contentious content. She says this proactive response works for everybody, including readers.

Dianne Touchell, author of upcoming A Small Madness, says applying an age-rating would be difficult. Her book is about teenage pregnancy and is deemed suitable for mature teen readers.  "Who would write the parameters and guidelines? And who would interpret those guidelines. There would have to be a starting point of some sort of moral consensus, which immediately makes me nervous.

"Content warnings, by their very nature, suggest a partiality toward conservatism, and I prefer to operate within the mores of inclusiveness - something that takes in the breadth and richness of all sorts of experience, good and bad."

Bookseller Jon Page of Pages & Pages Mosman tries to stay across the content of all children's books, no matter what the age. He's had some readers who have been too young to buy John Green's novel The Fault in Our Stars , about a teen cancer patient who falls in love, but says his job is not to censor but to provide advice.

The real issue is understanding, he says. "Children read at different levels throughout their lives. What it boils down to is each child's individual ability and maturity."