Jeff Kinney, author of "Diary of a Wimpy Kid," that best-selling "novel in cartoons," is the rare writer and cartoonist who considers the movie version of his book superior to the source, at least in one crucial way.

Jeff Kinney, author of "Diary of a Wimpy Kid," that best-selling "novel in cartoons," is the rare writer and cartoonist who considers the movie version of his book superior to the source, at least in one crucial way.

"What I'm happy about is the emotional content, which I think is absent from my book," he says. "This movie has got a lot of heart."

Disarming is the word for the Maryland born-and-bred Kinney. "I'm good to go, as long as you don't mind the sound of me noshing on a Klondike bar," he starts off a phone interview, fresh from a screening for family and friends in Ashburn, Va.

And disarming is the word for Kinney's work, too. His "Diary of a Wimpy Kid" became a publishing phenomenon and a continuing series because of its direct access to the middle-school mind. Kinney and 20th Century Fox are hoping to replicate that success on screen.

Kinney's Greg Heffley is a squiggle, mentally and physically. He finds being true to himself a challenge. He cares about his roly-poly best friend Rowley, a good-natured naif. But he feels disproportionately embarrassed when Rowley wears a Halloween costume that his safety-minded mother has festooned with reflectors.

Greg is a budding comic-strip artist. Too bad his comic art gets confused with a quest for middle-school fame.

With humor and without apology, Kinney presents Greg as a welter of youthful contradictions. The author's grasp of a boy's semi-formed heart and brain has won fans spanning several age groups. Sixth- and seventh-graders read Greg's journals as a reality check.

Grade-schoolers take them as an early-warning handbook. Parents read them for nostalgia sans tears. Kinney feels confident that adult as well as youthful fans will enjoy the movie and embrace its newfound qualities of feeling.

Some parents complain about Greg's many moral lapses, his devotion to laziness, his perennial lack of social responsibility. That, however, hasn't stopped 30 million copies of the laugh-out-loud books from being sold, lodging them semi-permanently atop the bestseller lists.

"There are plenty of kids in children's literature who are miniaturized adults, who always act heroically," says Kinney. "I wanted to create a character who's more relatable. He's not a bad kid, but he's not a fully formed human being. All the humor comes from his flaws. His character acts sort of despicably but gets you to root for him anyway. That's the trick."

The author has put his understanding of filmmaking into "The Wimpy Kid Movie Diary: How Greg Heffley Went Hollywood." It's a "making-of" book done in Wimpy Kid style. The paper is ruled like a composition tablet. The text is printed like a sample page in a penmanship class. And Kinney drops illustrations into the text like formalized doodles.

The movie diary, though, also contains behind-the-scene photos and close-ups of material like the "Westmore Warbler," the film's school newspaper. Kinney spells out all the intricacies of production in a manner even his youngest fans can understand.

But Kinney also learned about cinematic narrative.

"I really grew to appreciate the difference between book storytelling and movie storytelling," he says.

Greg's ambition to be popular became the script's organizing principle. "Nina Jacobson, who was one of the producers, would always say that any main character in a movie needs an 'I want song.' The audience should know right away what he or she wants... In my book it's a little bit nebulous, although, for Greg, popularity has always been an important motivating factor." What drove the script forward "was the friendship between Greg and Rowley."

Kinney tears up every time he sees the end of the movie, "and more so with each viewing. I just think childhood friendships are really powerful things and that's where I think the movie delivers, on their friendship."

The Wimpy Kid books follow the Larry David precept, "No hugging, no learning."

In the course of the movie, though, Greg evolves from "a likable jerk" into someone a bit less jerky.

"We preserved the character, kept his integrity, but also let him grow in a way that is pleasing to an audience," says Kinney. He concedes that introducing a girl reporter named Angie was part of an attempt "to appeal to as broad an audience as possible. But we really tried to make this character fit organically into this universe."

Angie puts Greg down "whenever he gets a little full of himself. She serves as the voice of the audience and a counterpoint to Greg."

Most important to Kinney, the film, like the book, is about "seeing childhood not through adult eyes but through a kid's eyes. The best compliment I could ever get as a writer is when a critic says he can't sense the adult behind the character. That's what I strive for."

He started the Wimpy Kid series back in 1998. (The first book came out in 2007.) He felt as if he was giving voice to a silent minority.

"When I was in junior high, I remember feeling that they just tucked us away, they were just trying to hide us from society as we made that transition between childhood and teenagerhood — or is it teendom? It felt so strange to me that there were six or seven years of elementary school and two years of junior high, then four years of college. It just felt like something was up."

Kinney says he had a "really pretty typical childhood experience" as he grew up in Fort Washington, Md., and accumulated raw material for his books.

"The stories that interest me (or strike me funny) are stories that fiction writers couldn't make up." For example, when his brother was in elementary school, one of the kids in a talent show "just roller-skated in a circle to a Bon Jovi song, for like three and a half minutes....I take moments like that and fictionalize them and make them serve my story."

For the Wimpy Kid books, Kinney draws on disappointments that have endured beyond childhood.

"Greg is a frustrated cartoonist, and that is something I experience even to this day. I don't feel I ever made it and that still gnaws at me." Kinney says he couldn't break into the newspaper comic-strip business "for good reason. My drawings weren't professional grade. I didn't have that consistency, that style that's required for the comics page. And that's why I ended up cartooning as a seventh grader. That's where I maxed out on my abilities."

Kinney lives in Plainville, Mass., with his wife Julie and their two sons, Will (7) and Grant (4). When he's not compiling anecdotes for Wimpy Kid books, he works as the creative director and executive producer of the kids' Web site, Poptropica.

"As a writer I've explored my own childhood very thoroughly. To know that what my children are going through now will one day be their childhood memories is exciting to me. I'm also excited to see if it might inspire me to write new material based on what I'm seeing of their childhood."

He doubts he'll have any trouble fitting "new material" into his ongoing series. He's always wanted his books to be timeless and universal. "I think the movie, too, works best if it seems like a celebration of childhood in general and not childhood during our era. I didn't want the film version to lock my books into a certain time and place. I didn't want it to a movie that would seem out of date 10 years from now."