Chicago ? Glenn Murray blushes a hearty shade of red when a cashier at a Chicago deli recognizes him: “Heyyyyyy!” the young man shouts gleefully — and loudly. “You’re the fart-man!”

Murray, an educator-turned-children’s author from Canada, is still getting used to the ruckus over two books he co-wrote. They feature “Walter the Farting Dog,” a flatulent pooch whose little problem saves the day time and time again.

The content may seem quirky and even off-color to some. But these days, potty humor is big in the world of popular children’s literature — from the “Captain Underpants” series to such best-selling titles as “Zombie Butts from Uranus!”

Parents jokingly call the genre the kids’ version of pulp fiction — or “poop fiction.”

“You’ve got to give kids something they want to read,” says Murray, who firmly believes that his smelly but well-meaning protagonist has become an ambassador for literacy.

It would seem that kids agree, since the genre’s books regularly appear on children’s best-seller lists.

Derek Morgan, an 11-year-old Chicagoan, recently picked up the second Walter picture book, subtitled “Trouble at the Yard Sale.”

“If you want to laugh,” the fifth-grader said at one of Murray’s book store appearances, “read this book.”

Kaylee Paul, a 6-year-old from Riverside, Calif., has latched onto Captain Underpants, a cross between a cartoon and a chapter book, written by author Dav Pilkey. Her favorite is about the “Big, Bad Battle of the Bionic Booger Boy.”

“I like to read it every day. I really, really do,” Kaylee says.

Kaylee’s parents say they originally bought her the Captain Underpants stories because, as an early reader, picture books became too easy. She likes the series so much that now her dad, Stan Paul, sometimes has to tell her, “That’s enough reading for today.”

Editors at Scholastic Inc., publisher of Captain Underpants, say that’s the goal — especially when it comes to kids who are “reluctant readers.”

Scholastic also publishes “Zombie Butts from Uranus!” by Andy Griffiths. It’s the sequel to “The Day My Butt Went Psycho,” a story about a 12-year-old named Zack whose back side is prone to detaching itself, running away and causing trouble.

Gail Glover, a mom from Port Crane, N.Y., bought the latter book for 9-year-old son Robbie, but later wondered if she’d made a mistake.

Among her objections were “descriptions of bodily functions that made my hair curl.”

“But of course, they solicited howls of laughter from my son,” Glover says, chalking it up to “a rite of passage in the development of his sense of humor.”

She notes, however, that her son still likes to read the “classics” — including the Harry Potter and “Lord of the Rings” books.

Those are the books he should be reading, say some parents who’ve persuaded their school libraries to take Captain Underpants and other titles off their shelves.

“I don’t want to be a prude about it,” says Sister St. John Delany, a nun who heads the School of Education at New York’s Pace University. “I just don’t think kids need to be exposed to that kind of language.”