Are celebrity children's books any good?

Will these children read Madonna's books to their own offspring?

Barack Obama captured the youth vote when he was elected in 2008, but can he capture an even younger audience with his children's picture book for ages five and upwards?

"Anyone can write a children's book - you can do it in your coffee break," says Maria Nikolajeva, professor of education at Cambridge University and director of its Centre of Children's Literature.

She's being sarcastic.

She has not yet read Barack Obama's book released on Tuesday, Of Thee I Sing, written in the form of a letter to his daughters, Sasha and Malia. But she's not optimistic.

So far as Professor Nikolajeva is concerned, the American president falls into the category of celebrity author - an amateur, whose books are easy for publishers to splash all over the media, but are rarely of any literary value.

"These are coffee-table books that adults read. I have never yet heard about a celebrity children's book that really was enjoyed by children," she says.

"There is lots of discussion about them when they first appear, but three months later they are forgotten. They come and they go. They don't have a lot of impact."

In the professor's view, books written by celebrities do no more harm than any other unwanted Christmas present.

"If children are bored they won't listen and they won't read it - they will go and get another book," she says.

According to Caroline Horn, children's news editor at The Bookseller, career children's authors were livid when the trend for celebrity authors kicked off a few years ago, and swallowed up publishers' marketing budgets.

"A lot of children's authors really resented this on the money side of things, when they've been working for years perfecting their craft," she says.

But there are now fewer of them, she adds, because publishers came to realise that an author's celebrity status, by itself, was not enough to make a book a success.

Barack Obama signed a $1.9m contract for three books, including this one, in 2004, when the trend for celebrity children's authors was near its height (though at that stage he had only just become a member of the US Senate).

He wrote it after the presidential election in 2008, and before his inauguration.

One of the purposes of the book is to pay tribute to 13 great Americans, from the painter Georgia O'Keeffe, to Albert Einstein (who became a US citizen after leaving Germany in 1933) to George Washington.

But how eager are children to read inspiring stories about adult role models?

According to Professor Nikolajeva, fiction generally has a greater appeal than non-fiction.

"If some kind of historical knowledge is transmitted through a fictional story, it usually makes a stronger impact than a book of facts," she says, while acknowledging that the boundary between fact and fiction is less clear for children than for adults.

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On the other hand, she foresees that some American children will feel proud that their president (if they are old enough to know what a president is) has written a book "for us".

She's keen not to pre-judge the book entirely. Despite taking a dim view overall of children's books written by celebrities, there are plenty of good books written by authors who pursued other careers she says.

Kenneth Grahame, for example, published The Wind in the Willows at the end of a long career in the Bank of England - a career that nowadays nobody remembers.

"If Barack Obama has written a brilliant children's book - wonderful," she says.

"Maybe, 50 years from now, he will be remembered as a children's author, not for being president."