These days in children's books, Diary of a Wimpy Kid is the It series. Abrams has more than 15 million copies in print of the four existing titles. Fox is holding open casting for a movie version, which has been fast-tracked for a fall release. And last week two Wimpy Kid books were nominated for a Nickelodeon Kids' Choice Award.

But other publishers aren't about to let the Wimpy Kid be king of the hill without a fight. Simon & Schuster is rolling out 75,000 copies of Rachel Renee Russell's Dork Diaries in June; catalogue copy describes it as “The Diary of a Wimpy Kid for Girls.” Like Wimpy Kid, it features lined paper and black-and-white drawings. And Houghton Mifflin Harcourt is printing 20,000 copies of James Roy's Max Quigley, a part-diary, part-novel Australian import that also uses childlike black-and-white drawings to help tell a boy's story.

Many booksellers, however, are skeptical about such Johnny-come-latelies. “For the first book or two out of the gate after one of those big successes, there's a hungry audience for it, but there's really a diminishing return after that,” said Kristen McLean, executive director of the Association of Booksellers for Children. “Rarely does a followup that's trying to hit the same niche in the marketplace hit it as successfully and authentically as the first series.”

McLean believes that subsequent books from other authors simply “split market share.” She added, “There could be a fantastic book in the following group, but oftentimes you're so fatigued by then that you just can't even stand to look at it.” For example, McLean loved Looks by Madeleine George, an eating-disorders novel that Viking published last June, but believes it failed to hit it big because of the “onslaught” of dark, teen-angst titles in the past few years.

Indeed, it's difficult to capture the magic—and broad appeal—of a book like Diary of a Wimpy Kid. “The way [Kinney] writes, the way he illustrates, perfectly captures the way an eight-year-old would communicate his thoughts,” said Charles Kochman, the Abrams editor who discovered Wimpy Kid back in February 2006. Abrams signed creator Jeff Kinney to write five Wimpy Kid books, one a year since 2007.

The Wimpy Kid copycats don't bother Kochman. “Imitations go with the territory. There's always going to be those who come along afterward to try to replicate what succeeds. But ultimately Wimpy Kid is going to be the brand name, the archetype.”

In many booksellers' eyes, the Wimpy imitators are, well, wimpy. Betsy Balyeat, children's book buyer for The Bookstall in Winnetka, Ill., did not order any copies of Dork Diaries or Max Quigley. She disliked the excerpt on the Dork Diaries' back cover: “I'm definitely not the kind of girl who curls up with a diary and a box of Godiva chocolates to write a bunch of really sappy stuff about my dreamy boyfriend.” Balyeat said, “I think girls deserve prose better than that.” She also disapproved of the Bratz doll—like cover illustration on the ARC, and, in fact, S&S plans to change the cover, following a suggestion by Barnes & Noble.

An interior from Dork Diaries.

The problem is not the diary format itself. Booksellers cite past journal-style successes such as Meg Cabot's Princess Diaries and the more recent Ellie McDoodle series by Ruth McNally Barshaw. “You're basically telling a story through a child's eyes,” said Kenny Brechner, owner of Devaney Doak & Garrett Booksellers in Farmington, Me. He calls the Ellie McDoodle series “fantastic, original,” despite the similar diary format.

“The more the merrier, as long as the quality of writing is still there,” said Heather Doss, children's merchandise manager for Bookazine. “There's no point in putting out books that the kids are going to look at and roll their eyes. Kids are very, very smart. They know when they're being taken advantage of.”

Brechner observed that kids, including his own teenage son, are skeptical when they see a lookalike to a kid-lit hit. For instance, a host of vampire and other supernatural titles has arisen on the heels of the runaway popularity of Twilight.

Still, sales reps often describe a book to booksellers as a “blank meets blank” title, said Doss. That's true for agents, too. When agent Daniel Lazar sent Dork Diaries to Liesa Abrams, executive editor of S&S's Aladdin imprint, he called it “The Princess Diaries meets Wimpy Kid,” Abrams recalls. Last spring she bought the book at auction; it comes out June 2.

Sometimes editors are unaware of a trend when they buy titles. Ann Rider, executive editor of Houghton Mifflin Harcourt Children's Books, acquired Max Quigley because she liked how the author wrote from the bully's point of view, not because of Wimpy Kid. “If I'm on the bandwagon, I didn't know I was getting on it,” she said. “My goal is not to be derivative.”

Of course, many high-quality books, including the subsequently imitated Harry Potter stories, contain derivative elements. The difference, said Brechner, is influence vs. imitation. After all, he points out, “There are only so many narrative devices under the sun.”