Jeff Kinney has the slightly fazed air of somebody who cannot quite believe what is happening to him.
Kinney is one of the most successful children's authors on the planet and today he is digesting the news that his latest book, Diary of a Wimpy Kid: Cabin Fever, has leapt straight into the No 1 slot in the British children's best-selling book charts. Its predecessor, Diary of a Wimpy Kid: The Ugly Truth, published last year, was said to have sold at the rate of one book every 11 seconds. "It is still pretty hard to take in," Kinney admits with a lopsided grin. "I feel like I'm watching it happen to someone else."
This is the sixth Wimpy Kid book. The first was published just four years ago by a small American art-book publisher with a print-run of only 15,000.
Like all the others, the new title describes the ups and downs, trials and tribulations of the everyday life of Greg Heffley, a likeable, self-obsessed 12-year-old desperate to fit in at school, hugely impatient to grow up and tormented by his amoral older brother, his pesky baby brother and his well-meaning parents. This time, Greg and his family are snowed-in over the holidays, leading to all kinds of domestic mayhem.
The Wimpy Kid format is simple. Each book is full of handwritten notes to make it look as though it is Greg's diary and the pages are peppered with cartoon illustrations of his day-to-day life. The plots are paper-thin but the jokes come thick and fast - and the results have been staggering.
The books have been translated into 30 languages and have sold more than 50 million copies worldwide. The first two titles have been made into movies which, while they may not have appealed to the critics, made more than US$147 million ($189 million) at the box office. Kinney himself was named one of Time magazine's 100 most influential people of 2009, something he actually thought was a practical joke ("I'm not even the most influential person in my own house," he said at the time).
Brought up on a diet of Donald Duck, Uncle Scrooge and The Far Side, Kinney dreamed as a student of becoming a newspaper cartoonist but says modestly that his "lack of talent as an illustrator" put paid to that ambition. Instead, he took a job after college as a graphic and layout designer on a local newspaper and went on to conceive and set up Poptropica, an educational gaming site for children. As if to confirm the impression I've been getting that his global success as an author has not quite sunk in, Kinney tells me he still works for Poptropica full-time.
"They are very understanding when I need to go on book tours but when I get back to my normal life, it is nine-to-five every day. I only work on my books at nights and at weekends. It is really just like a hobby," he says, albeit an incredibly time-consuming one. Each book takes nine months of evenings and weekends to finish, leaving little time for anything else.
Luckily his wife, Julie, is "very supportive" and his sons, Will, 9, and Grant, 6, enjoy watching him draw - "so I spend time with them that way". A self-confessed big kid, who would happily eat "junk cereal" for every meal, he has also just become Cub-Scout master for his boys' local troop in Plainville, Massachussets - which he is "very excited about".
When Kinney first had the idea for the Wimpy Kid, he thought it would be a one-off nostalgic book for adults. "I never thought I was writing for kids at all," he explains. "It really shocked and unsettled me to hear kids were buying the books. If I'd known I was writing for kids I might actually have spelled things out a bit more and that would probably have killed the appeal."
He thinks the slightly knowing, adult perspective of his characters is one of the qualities children find appealing. "Kids can sniff out when they are being preached to and they don't like it," he says. "So while my books aren't amoral they are not infused with morals or a message either and kids like that. They also like the fact that Greg is awkward and imperfect. He's not better than them at everything; he's struggling to manage life, just as they are."
The look of the books is as important as the storyline and characters, he says.
Kinney draws a parallel between Greg and Holden Caulfield of The Catcher in the Rye: "In both cases you have a slightly unreliable narrator who is very cocksure and certain that his view of the world is the correct one - there might well be an unconscious relationship between my character and J.D. Salinger's."
Holden Caulfield made only one literary outing but Greg's appearances in print have become an annual event (publication day this year was dubbed "Wimpy Kid Wednesday" by the book trade). But while there is another movie in the pipeline, Kinney is not planning to carry on the series indefinitely.
"Success has come so quickly I'm reluctant to think about bringing it to an end, but every creative endeavour has a lifespan and the best creators know when to end things. I think the optimum length for the series will be somewhere between seven and 10 books, a bit like Harry Potter. I don't want to overstay my welcome."
Diary of a Wimpy Kid: Cabin Fever (Penguin $17.99) is out now.