Harry N. Abrams announced late Tuesday that it has increased the print run for the October 12 release of Jeff Kinney’s Diary of a Wimpy Kid: Dog Days from three million to four million, based on strong demand. This makes the fourth installment of the cartoon-illustrated series the largest first printing for any children’s book this year. Since April 2007, when the series debuted, the publisher has produced a combined 21 million copies of Kinney’s other titles: Diary of a Wimpy Kid; Rodrick Rules; and The Last Straw; along with the Diary of a Wimpy Kid Do-It-Yourself Book Journal.

Abrams has kept the latest book so secret that not even the buyers for Borders and Barnes & Noble have read it. When asked in a recent interview to provide any clues to the plot of Dog Days -- the first to feature Greg Heffley in the summer, outside of school -- Kinney offered only, “Greg gets a pet.”

Adding to the buzz, next April Twentieth Century Fox will release a full-length movie version of the first book (starring 11-year-old Zachary Gordon of TV’s How I Met Your Mother). Kinney has been on set for about half of the shoot in Vancouver, which began on August 12 and wraps up next week. If the first movie succeeds at the box office, Fox and Kinney plan to turn more of the books into films.

Also this week, Borders announced that it is exclusively selling Wimpy Kid T-shirts with an image of Greg Heffley with a word bubble that kids can decorate using a washable marker that comes with the shirt (the ink washes off so that kids can redecorate the shirt after each wearing). The price: $9.99 alone or $5.99 with the purchase of Dog Days. On release day, Kinney will appear at a ticketed Borders event in Providence at the Rhode Island Convention Center. Then, the day after shooting wraps on his movie, he will hop on his Wimpy Kid-decorated bus for a bookstore tour (nine appearances in seven cities). "I am looking forward to it," Kinney said. "It's going to be an endurance marathon."

For more on the book's release, including an interview with Kinney, see this Thursday's Children's Bookshelf.