A Laughing Matter : Tired of silly knock-knock jokes? Take heart. Kids with a sense of humor become happier adults.

Denise McKnight puts her thumbs in her ears and sticks out her tongue. Her 4-year-old daughter, Jade, falls down laughing. “And she tries to do the same face back,” says McKnight, 29, of Los Angeles.

These small, silly moments have a big payoff.

A healthy sense of humor will help a child make friends, cope with stress and put her in a positive frame of mind. Down the road, this will allow her to be more productive in school and more focused on the job, says developmental psychologist Paul McGhee, who has published 11 books on humor.

What can parents do? Lighten up and allow interesting and novel things to happen. Make time to read and tell funny stories. Be playful with your kids. And show them you can see humor in adversity.

“If you are having a bad day or have burnt the dinner and you find some way of making light of it, then the kid is exposed to the idea that even when things go wrong if you find something to laugh at, well, it’s not so bad after all,” McGhee says.

Children’s humor, which follows rather universal stages, parallels their intellectual and social growth. “Once a child has mastered some idea or concept, the child can then appreciate a distortion of that concept,” says Amelia Klein, associate professor of professional studies at Wheelock College in Boston. She is editing a book on children’s humor.

Once a toddler understands that cups are for drinking, he finds fun in holding a cup up to his ear and pretending it’s a telephone. “They like to turn their reality around--screw it all up. So they might put shoes on their hands or socks on their ears,” McGhee says.

For children and adults, humor is based on the incongruous, exaggerated, silly or unexpected. Preschoolers find it amusing to intentionally call an object by a different name. This reflects their growing interest in language. Made-up nonsense words are another source of laughter.

What may strike a parent most about the preschool stage is the toilet humor that starts about 3 years of age and seems to last forever. According to experts, it peaks about 4.

“My theory is that children are dealing with the anxieties and frustrations and unpleasant experiences they had going through toilet training,” Klein says.

“Sometimes it is used to get attention and provoke adults--a testing of the rules,” she adds.

Lynn Bommer, who teaches early childhood development courses through UCLA Extension, describes a round of jokes she heard while driving her two sons’ school carpool. “It started with ‘poo-poo on your hand’ and everybody laughed. Then ‘poo-poo on your arm’ and everybody laughed,” Bommer says. “It went around until it finally wore itself out. My son said, ‘throw up on your head.’ And then gales of laughter and they started the whole thing over.”

Experts advise an annoyed parent to just ignore vulgar jokes. Children can be asked not to tell bathroom jokes in certain situations or around specific people.

At about 5 or 6, kids make their first attempts at telling real jokes even though sometimes they fall a little flat. “They don’t understand enough about the nature of the joke or structure of humor to get it right,” Klein says.

Sherry Wallace of Los Angeles says her first-grader likes to make up jokes.

“But they end up being silly nonsensical stuff like, ‘Knock knock.’ ‘Who’s there?’ And she’d say ‘giraffe.’ I’d say ‘Giraffe who?’ Then she makes up these silly things like ‘giraffe has spots’ and giggles and walks off.”

About a year after they start experimenting with riddles, children are able to understand, memorize and repeat them correctly.

When they are 6 or 7, kids make a developmental leap and are intellectually able to keep two ideas or word meanings in mind simultaneously. Word plays, puns and double meanings are amusing to first- and second-graders.

A favorite riddle of second-graders is, “What would a polar bear telephone operator say?

“Have an ice day.”

Telling riddles has another appeal for children: They know the answer and the adult doesn’t. With their friends, kids find sharing jokes is a way to be liked.

“Kids who have a good sense of humor are more popular and more sought out,” McGhee says. “Kids like kids who can make them laugh or they can share laughter with. It is a valuable communication skill.”

In about third or fourth grade, children have mastered the joke convention and find it fun to switch the rules on riddle telling. Jokes like this are popular: “What did the apple say to the banana?” The answer: “Nothing. Apples don’t talk.”

Humor also reflects social development. Some elementary school kids find it hilarious to make noises like passing gas or burping. Such antisocial rebellious behavior, which appalls adults, is a way of impressing friends.

Indeed, McKnight and her husband, James, have a lot to look forward to. But right now they can delight in 3-year-old Jade’s antics, including her imitation of Grandma.

“She puts a pencil to her mouth as if she were smoking,” recounts McKnight with a laugh.