He writes, he draws, and he's very funny!

Have you ever had a friend who was sad? Piggie has, and she decides that it's up to her to cheer him up.

In the children's picture book "My Friend Is Sad" (Hyperion; $8.99), author/illustrator Mo Willems tells the story of an unhappy elephant named Gerald who is having a bad day. So his best friend, Piggie, decides to boost his mood – by dressing up as a cowboy, a clown, and a robot.

Nothing works. That's because Gerald doesn't recognize Piggie in the costumes.

When his friend returns without any disguises, Gerald tells her everything that had happened – and that he's happy Piggie has "finally" arrived.

"I need my friends," Gerald says.

"You need new glasses," Piggie replies sarcastically.

Mr. Willems, who lives in Brooklyn, N.Y., with his wife and daughter, has won major awards for his children's books. His first, "Don't Let the Pigeon Drive the Bus!" published in 2003, earned a Caldecott Medal of Honor, which is awarded annually by a division of the American Library Association to "the most distinguished American picture book for kids."

He won a second Caldecott the following year for his book, "Knuffle Bunny: A Cautionary Tale." (It's pronounced "ka-NUFFLE," which means "cute and cuddly" in Dutch.)

The Elephant & Piggie series is Mr. Willems's first attempt at "easy readers" – books geared to children ages 4 to 8. "I tried to make sure all the characters can be drawn by a 5-year-old," he says on a recent visit to the Brookline (Mass.) Public Library, where he was promoting his latest book. He thinks that the simpler the drawing, the more expressive it can be.

Mr. Willems also kept the language simple, limiting the use of different words to fewer than 60. The idea, he says, is to focus on the words and the body language of the characters.

Although Elephant Gerald wears a frown throughout most of the latest book, the opposite can be said of most of the book's readers. Nine-year-old Shirley Hecht of Brookline was all smiles after acting out the role of Piggie during a reading with her favorite children's author, who played the part of Gerald.

"His books are really funny," she says, adding that she likes "Don't Let the Pigeon Drive the Bus!" best – "because it has a way of making me laugh."

Like many kids, Mr. Willems started drawing when he was in elementary school. His favorite characters were Charlie Brown and his dog, Snoopy. The future author/illustrator, who refers to himself as a cartoonist, also drew his own characters and "put them in different situations," he says. "I'd think, 'What do [the characters] look like in silly shoes?' Then I'd draw them."

Not every drawing was great, he adds of his early work: "I had to get my bad drawings out first." He likens becoming a good illustrator to becoming a good baseball hitter: "You start out slow, but you get better over time."

With time came confidence, too, a personality trait that best describes Piggie in Mr. Willems's second Elephant & Piggie book – "Today I Will Fly!" (Hyperion; $8.99) – which was released at the same time as "My Friend Is Sad."

In the second adventure, Piggie, ever the optimist, proclaims that she will "fly, fly, fly."

Gerald isn't convinced that pigs can fly, but after seeing Piggie take flight with the "help" of a pelican, he has a change of heart.

"Tomorrow I will fly," Gerald says.

"Good luck!" Piggie replies, poking fun at her friend.

Mr. Willems recommends that if you like to draw – draw! "Do it and show it to friends, your mom, a teacher. If they don't love it, try to do it better next time. It's better to complete something that's not great than it is not to finish something that is."

He adds that the best part about drawing for a living, as opposed to following another profession, is that kids of any age can do what he does, starting today.

"You can't be an astronaut right now," he told the group of kids at the library, most of whom were 6 and 7 years old. "You can't be a balloon salesman right now. But you can draw. And that's very cool."

Indeed, it is.