J.K. Rowling wrote hers because she was broke. P.B. Kerr has written his first children’s book for an equally compelling reason: he was worried that his children were becoming couch potatoes.

Preferring television and computer games, they did not rush to the bookshelves. But perhaps, he thought, they would read a book written by their father. Several months and 100,000 words later, the exercise has had a very happy ending.

William, 11, and Charlie, seven, are thrilled with The Akhenaten Adventure. And P.B. Kerr, better known as Philip Kerr, one of Britain’s most successful adult thriller writers, has found that his indulgence has paid off handsomely.

Steven Spielberg’s Dreamworks studio is “hammering out a seven-figure deal” for the rights to The Akhenaten Adventure, the Hollywood film magazine Variety reported.

The deal “is unusually lucrative for a children’s book”, the report added — and it certainly is. J.K. Rowling sold the film rights to her first Harry Potter book for a reported £30,000.

More unusually, The Akhenaten Adventure has not even been published. With children’s literature experiencing a golden age, it is expected to cause a scramble when the rights are offered at the ongoing Frankfurt Book Fair.

Kerr, 47, says: “I had made the mistake of buying William a PS2 and in an effort to wean him off that and the PC, I started to write a book which I hoped would stop him and in turn his younger brother, Charlie, from becoming complete couch potatoes.

“I had always wanted to write a children’s book, only I could never think of a subject: and then, almost at the same time as I was worrying about William’s not reading very much, I thought of a story. I read a lot when I was young but, of course, I didn’t have all these temptations.

“I want my children to be as literate, if not more literate than me, but I can’t see it happening so long as they are perched in front of the television all the time. Children are missing out on that very important other world, the imaginative world that you can create for yourself.”

The Akhenaten Adventure was inspired partly by The Arabian Nights and concerns the exploits of a young boy and girl living in London, New York, Cairo and at the North Pole.

Akhenaten, whose ghost appears to the children, was the heretic Pharaoh who was married to Nefertiti in Egypt 3,500 years ago.

Kerr says: “I read the boys the first chapter and William soon said that he wanted me to stop so he could read to himself. Charlie just walked away and didn't show any interest. But after a few days, he came back and begged me to carry on.”

Kerr, who has published a dozen adult books, says writing for children was liberating because he could throw out all the rules and let his imagination roam free.

He is now planning a series called Children of the Lamp with the same two characters.

The next book will be called The Blue Djinn of Babylon, named after ancient Babylon’s famous gates.

“Each book will be titled alphabetically. It's theoretically possible that there could be as many as 26, but don’t hold your breath,” he says.

Kerr is no innocent in Hollywood. He has sold several adult books there, including A Five Year Plan for which Tom Cruise paid $2.5 million.

Kerr says that writing for children as P.B. Kerr and for adults as Philip is no affectation.

“I am trying to avoid confusion. I would not want children picking up my adult books, which are quite colourful in places.”