Children’s books are being treated with renewed respect,” says Francesca Simon, the creator of Horrid Henry, the primary school antihero. “When a long article is written now about Jacqueline Wilson, she is treated like a writer. That wouldn’t have happened a few years ago.”

Simon is among those writers for children — well represented at this year’s Sunday Times Oxford Literary Festival — who reward attention. She produces stories of wild humour underpinned with an imaginative intelligence and verbal precision that also keep adults entertained. The idea that adults might enjoy children’s literature has become fashionable, which is one of the reasons why attention is being paid to it.

Publishers bandy about the term “crossover” for a book with both adult and child appeal. But as this year’s festival authors point out, it is nothing new. “Thirty years ago there were K M Peyton, Ursula Le Guin and Jane Gardam,” says Adèle Geras, the author of the Egerton Hall trilogy. “What has changed is the marketing, which follows on from much larger advances for children’s authors — sometimes ridiculously large. Publishers feel they have to pay in case they miss the next Harry Potter. That’s why you get all these six-figure deals for fantasy trilogies.”

The concept of crossover affected the destiny of another festival attendee, Mark Haddon, whose widely lauded narrative of an autistic boy, The Curious Incident of the Dog in the Night-time, won the Whitbread Book of the Year prize. It emerged as an adult book but was originally signed up by children’s editor David Fickling at Random House. Fellow imprint Cape seized the chance to join in and publish an adult edition.

Michael Morpurgo, the children’s laureate, argues that “every good children’s book” can appeal to adults as well. The books of his childhood bear this out. “I recently reread the Just So Stories and they are as wonderful as they were when they were read to me at about four. Crossover is an idea of marketing people and I am suspicious of it. There are too many headlines about advances, and publishers will follow the seam that seems to be producing the most gold. Every writer has to plough his own furrow.”

Philip Pullman concurs: “Children’s publishers are afraid of what accountants will allow, and look for the next Harry Potter. But nobody was looking for the first Harry Potter. The thing is not to be cautious, but to take chances, be courageous.” When his own Northern Lights was published it was a much longer book than was thought to work for children, and not a conventional fantasy. Current practices may, he thinks, be unwise. “The whole structure of the book world works against the long apprenticeship that I and other writers had — writing a lot of books without making a lot of money, and slowly establishing a style.”

Pullman has, of course, helped stoke a fashion for fantasy that other publishers follow. He uses the genre because in today’s “culture of anxiety” it “allows child protagonists to have interesting, exciting things to do. Otherwise if you put children in danger nobody will publish it. You couldn’t get Swallows and Amazons published these days”. There is also a problem with modern devices that interfere with plots. “The mobile phone is a curse for writers of fiction. Now children in danger would just phone someone. You have to say the batteries are flat.” In Lionboy by Zizou Corder, exactly this happens. But Louisa Young and her 11-year-old daughter, Isabel Adomakoh Young, who wrote the book under their joint pen name and are also appearing at Oxford, use the phone in clever plot twists so that it doesn’t cramp the style of their young hero, who can speak to cats and lions and travels with a circus in pursuit of his kidnapped parents.

Although fantasy is riding high, Pullman cites honourable exceptions. “Some authors tell it like it is. Jacqueline Wilson and Anne Fine (both at the festival) are awfully good at the domestic. I like to do what Scott called the ‘big bow-wow’ stuff. I can’t do quotidian.”

Crossover books may fit a wider category than publishers generally acknowledge. Ted Dewan, creator of Crispin the Pig and one of the festival’s picturebook authors and illustrators (along with Jez Alborough and prolific author Vivian French) points out: “The books that really have to have adult appeal are the toddler books — because those are the books adults have to read over and over again. I am waiting for a Harry Potter of picturebooks.”

For adults and children who prefer non-fiction, television presenter Nicola Davies will be at Oxford discussing her book about wild animals. There are also two days of events on Tuesday and Wednesday, open only to schoolchildren and the home-schooled, offering madcap humour (Jeremy Strong and Kaye Umansky), thrills (Anthony Horowitz and Gillian Cross), poetry (John Foster), real-life drama (Lucy Lethbridge on Ada Lovelace), sophisticated adventure (William Nicholson and Sally Prue) and writers so versatile and prolific they cater for everyone (Fine and Mary Hoffman). As Morpurgo says: “These days there are books for everyone. Nobody has an excuse not to read.”

All the authors mentioned are appearing at The Sunday Times Oxford Literary Festival; dates, times vary.

Nicolette Jones will chair Writing for Children, Writing for Adults? on Sunday, March 28, at 2pm. To book, call 01865 305305

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