Image caption Jeff Kinney has written 13 books in the series, sold in 140 countries

He's one of the world's most successful children's authors - selling 200 million copies of his Diary of a Wimpy Kid series and meeting three US presidents along the way. But Jeff Kinney admits he struggles to get his own children off video game Fortnite.

"They are like most kids," he tells the BBC's Victoria Derbyshire programme of his two sons, aged 13 and 16, "you have to prod them to read".

"We are victorious if they spend less than five hours a day on screens at the weekend," he jokes.

Encouraging children to read, though, comes naturally to Kinney.

His Wimpy Kid series - now encompassing 13 books and sold in 140 countries - has been credited with inspiring many young people, especially boys, to read.

Image copyright ™ and © 2018, Wimpy Kid, Inc. Image caption The books tell the story of middle-schooler Greg

Presented in a handwritten font - with Kinney's trademark cartoons - the books tell the story of middle-schooler Greg, his flawed family and his best friend, Rowley.

"I feel a huge responsibility to encourage literacy," the author says. "I see that the more people read, the higher their quality of life is and it turns them into lifelong readers."

He says he has been shocked to find many children in the US, where he is from, "don't have a single book in their home".

"People underestimate how valuable a kid finds a book," he says, adding that he has organised book fairs where children can take home three books each.

"The kids are so surprised when they realise they can keep them. Books are seen very much as a treasured object."

'Another seven books'

Kinney came up with the idea for his Wimpy Kid books in 1998, taking eight years to show it to a publisher.

But now, two decades on, he believes he has another seven books in the series still in him.

"I am aiming to write 20 - that's my hope," he says, adding that it's made easier by his choice to freeze his characters in time.

"I realised around book five," he says, "that these are cartoon characters, so they don't have to age.

"People don't want cartoon characters to change. Bart Simpson has been around for 25 years - and still going strong."

Image caption Kinney owns a book shop as well as writing the Wimpy Kid series

Kinney juggles writing with the day-to-day running of a book shop in Plainville, Massachusetts, where he lives.

He says he decided to open it because the town "needed a facelift".

It's since been visited by top authors such as David Walliams - whose work he says he admires.

Kinney is also working to develop the Wimpy Kid books into an animated series.

"I have written two episodes so far," he says. "I am trying to get at the truth of childhood and to make it as deep as it can be considering it's a cartoon TV show."

And there perhaps lies the key to his books' success.

"The root of it all is childhood experiences," he says, overjoyed that his work is read across the globe.

"We have a lot more in common country to country than we might think. We share the same childhood in many ways all over the world.

"It's really excited me over the past few years, that kids in Turkey, China and New Zealand all see something in my books."

This has then fed back into his work.

"In the past, when I first started writing the series, I would have told a Thanksgiving story or a Christmas story," he says, "but they aren't inclusive so I try to avoid that now - perhaps make it a birthday one instead."

Image copyright L’OSSERVATORE ROMANO Image caption Kinney says the image of Pope Francis reading his book is one of his favourite photos

Kinney himself is Catholic, and says he was left "stunned" after being sent a photo of the Pope holding one of his books after it had been translated into Latin.

"I love that photo," he says, saying such moments - alongside meeting US Presidents Barack Obama and George Bush - are "weirdly out of joint" with family life in small-town America, where he continues in his fruitless attempts to reduce his children's use of technology.

"It's common sense when they have been on their screens too much - you can tell when it's too much," he says.

"But banning is a problem for kids because of the social side of things - imagine if you knew your friends were talking and you were missing out? That's hard."

He may be losing the battle with his own children but at least he can rest assured that his Wimpy Kid series is keeping other parents' kids from reaching for their phones and tablets - and perhaps sparking a love of reading that they can carry into adulthood.

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