I wanted to publish my book under a different name," says the DJ and household name, "precisely because I didn't really want to be part of this conversation about celebrity authors."
But Simon Mayo (pictured, left), Radio 2 presenter, soon discovered that anonymity was not an option. His children's book, Itch, about 14-year-old Itchingham Lofte, who has decided to collect all the elements in the periodic table, was published earlier this year to general, if slightly surprised, praise.
"I was there when Madonna did her book launch on top of a hotel and read her book," the DJ says. "Over the past 10 or 12 years, I've interviewed so many celebrity authors - some good, some less good - that I didn't really want to be part of that. I wanted the book to be considered on its merits."
A nice idea, perhaps, but a little romantic in the frantic world of publishing, where hundreds of thousands of books have to fight for the shrinking amount of space in bookshops and where even Amazon's extensive internet offerings are aimed at those who already know what they like.
Publisher Random House was certainly having none of it. The company - whose children's authors include Katie Price (the model formerly known as Jordan) and England and Arsenal footballer Theo Walcott alongside best- sellers Jacqueline Wilson and Philip Pullman - knows the power of a name.
"We were quick to persuade him he should have his name on it," says Clare Hall-Craggs, publicity director at Random House. "It is very tough breaking in a debut author. Anything that helps open a door to retailers is worth using."
But Caroline Horn, children's news editor for The Bookseller magazine, understands Mayo's initial reluctance. "Mayo was right to be worried about that taint of writing a celebrity book," she says. "Because everyone does think, `Oh, not another celebrity book,' and reviewers can be reluctant to read it on that basis. But in his case, it's actually a very good first book, whoever it was written by."
Celebrity publishing is not new. In 1946, Elizabeth Taylor, then just 14 but already a film star, published a book about the adventures of her pet chipmunk, called Nibbles and Me. The Old Man of Lochnagar by the Prince of Wales (pictured, right) came out in 1980 and Sarah, Duchess of York, had her first Budgie the Little Helicopter book published in 1989.
Then, in 2003, Madonna signed up with Penguin to write a series of five children's books. Celebrity-authored children's books had gone mainstream and sales began to rocket. Publishers could not - and still cannot - get enough of them.
Madonna's first book, The English Roses, and the second, Mr Peabody's Apples (dedicated "to teachers everywhere"), sold a combined 1.2 million copies worldwide in 2003. Both books debuted at number one on The New York Times children's picture book best-seller list.
Not in it for the money
So what is it about the pound;776 million children's book market that appeals to celebrities?
Madonna says it is not the money. She told Oprah Winfrey that, on the contrary, writing the stories - inspired by her daughter, Lourdes, then aged 6 - was the first time she had worked without thinking about the cash. "I knew that I was going to write these stories, and I wasn't going to make any money off of them," said the singer in 2003. "I wanted to take all the money that I made from the books and give that money to children's charities.
"For me, this is an amazing concept, because my entire career, for the past 20 years, every time I've taken a job, I went, `How much money is it going to pay me and how much time is it going to take me?' . It was incredibly liberating to write these stories and to know that my gift was that I was going to give these stories to people."
She is not alone in being inspired by her child; Barack Obama's book Of Thee I Sing is subtitled "a letter to my daughters".
"A lot of people writing for children start because they have fond feelings about books for children and want to write for their own children," says Julia Green, director of the MA in writing for young people at Bath Spa University and herself a children's author. "It is about sharing stories, that feeling of wanting to connect. There is nothing more powerful than that as a motivating force."
But as honest, honourable and human as wanting to pass on the wisdom of your experience can be, it does not necessarily result in a great children's story. And it is also important to ask whether children should be reading them at all. Are they good or bad for literacy?
The answer, of course, is not simple. Professor Maria Nikolajeva is director of the Research and Teaching Centre for Children's Literature at the University of Cambridge. She would not count people such as Charlie Higson or David Walliams as celebrity authors, because they were already making a living as writers before turning to children's fiction.
"When I say celebrity authors," she says, "I'm thinking of people like the Prince of Wales. I think they sincerely believe they are writing something original; I am sure they have good intentions. But I have looked at quite a few celebrity books in the interests of research and they are mostly very bad.
"It's extremely difficult to write for children because you need to shed your adult experience and adult way of thinking. Telling a primitive story in a simple language, which is very explicit or didactic, which doesn't leave gaps for imagination, does not work."
While there seems to be little variation between famous and non-famous people in why they want to write - or how good they are - there is one difference: the ability to get published.
"People in publishing say real talent will always rise to the top, but that is not necessarily true. Some books are easier to sell," says Green.
She can see why publishers want to shout about their big names in the hope of attracting previously uninterested new customers. But she points out that the celebrity-led clamour to expand their market does a disservice to existing book buyers, who get a narrower and narrower view of what is out there.
"Certain authors get promoted, and books that are really wonderful, well written, creative, with an imaginative story by unknown authors are not," she says. "The coverage of children's books in newspapers is tiny. That's why it bothers me when celebrities get the limelight. There is so little coverage, it is a shame that it's going to those people rather than really high-quality children's authors."
But Alison Baverstock, a former publisher and course leader for the publishing MA at Kingston University, thinks this view is flawed. "These are real books. There is a market for them. It's a bit popular to dismiss them and say they're rubbish, but they offer a shallow end to reading for non-reading children.
"People got hot under the collar about Katie Price being nominated for a children's book prize (Katie Price's Perfect Ponies was nominated for the WH Smith children's book award in 2008), but they forget it was children who voted for it. Children are just as interested in celebrity as the rest of us."
This, then, is the key. If children want to read celebrity-authored books then there is little reason to stop them. Any reading, it would seem, is better than no reading.
Julia Eccleshare, co-director of the Centre for Literacy in Primary Education, which runs training courses, projects and conferences for teachers, says we should not get too hung up on the idea of great literature, and if celebrity authors are a way of engaging children with reading then that should be more than enough.
"It's a hook," she says. "I don't think teachers are likely to use celeb books as a class resource or get a day's activity out of them because they are often quite shallow and usually don't have great literary style. But I'd have them in the classroom reading-for-pleasure box, particularly if they're books like Theo Walcott's football books.
"They are perfectly good short stories, and boys might pick them up because they think Theo knows about football. With all reading, teachers will want to take children on, but you have to start where they are comfortable. Books in classrooms can't be too austere - that doesn't help anybody."
Whatever gets them hooked
In fact, says Alison Peacock, head of the Wroxham School, a primary in Hertfordshire, the mere existence of celebrity authors could have a positive impact on reading and writing. She wants all her pupils to see themselves as potential authors and the school publishes children's work and encourages them to share their writing. She points out that celebrity authors help endorse this message, because they are famous for doing something else but also want to write.
"I agree that the real children's classics, which really draw you in and have compelling storylines, are by fantastic authors such as Philip Pullman. But anything that encourages children to read is helpful," she says. "You wouldn't want to only have populist literature, just as you wouldn't want to only eat junk food. But once in a while it will have no effect on your health, and the job of a teacher is to entice and tempt children to move on to other kinds of literature."
Unlike most junk food, however, it would seem that the quality of celebrity-authored children's books is on the rise. Horn of The Bookseller says that the wave of signings beginning with Madonna saw publishers spending lots of money on recruiting big names. There was just one problem: they did not necessarily write good stories.
"If you look at who is being published now - Mackenzie Crook, David Walliams - they are good," she says. "Publishers got their fingers burned first time round, so second time around they are doing it quite well and publishing good books. But the way the economics of publishing is going, if you have a name that is recognised, it really does help.
"Authors who aren't big names are having a tougher and tougher time on the high street, because there has been this shift in focus."
In short, publishers now need writers who are both good and known. And that is what is increasingly appearing in school libraries and bookshops.