The things that children find funny tell us a great deal about their level of development and what is on their minds. There is a connection between the 2-year-old who bursts into a fit of giggles upon hearing the nonsense phrase “bottle, battle, bittle” and the young adolescent who laughs at the bawdiness of an off-color joke.

The specific things children laugh at tell us which developmental tasks they are struggling with. That is a pattern that runs throughout childhood. It explains why 3-year-olds, who are often still mastering toilet training, are enthralled by “bathroom” humor while 7-year-olds, who no longer consider toilet-training an issue, think such jokes are just stupid.

Laughing and smiling are among the most human of behaviors. A twelve-hour-old infant will shape his mouth into what looks like a smile at the smell of a banana or other sweet food. Our nervous systems appear to be wired to make us smile. No learning or imitation is needed. True laughter, which is more complex, does not appear until a few months later.

Children learn some very complex things during their first dozen months, starting with the realization that they are separate individuals from their parents. Soon they begin to understand that objects and people exist, even when they are out of sight. This is a very profound realization. When Mom leaves the room, she is doing something else and will eventually return. A toy that is placed behind a cardboard barrier can be obtained if you reach around or over the barrier. By reaching for that toy, the child shows that he understands the concept that people and things have a physical existence even when they are not seen. (The first time I tried this test on my 6-month-old son he tried to eat the cardboard barrier!)

Few things elicit as much laughter from a 1-year-old child as a game of peekaboo. Yet a 6-month-old will barely respond to the game, and a 6-year-old will find it boring. Laughing at peekaboo is a marker for a certain level of intellectual development. The intensity of the 1-year-old’s laughter tells you that he or she “gets it”: That’s my mother behind those hands! It is a realization that would have eluded the child only a few weeks or months earlier.

The game of peekaboo still works if done in silence. Watching the mother’s face disappear behind her hands excites the child, who knows that the mother is back there and predicts that she will reappear. It is a tense situation. When the mother’s face comes back into view, the child is relieved and laughs with excitement. What was scary is now fun, for the child can predict the future. If the mother keeps her face hidden for too long, however, the child’s tension will turn to fear, and the child will cry.

Once children understand a concept, they take great joy in playing with it. Two-year-olds who are beginning to master the intricacies of language will giggle uncontrollably when they hear a combination of words and nonsense syllables. They understand that the nonsense syllables are different from the words. The sounds are out of place. They are funny.

Other things that are out of place will get the same laughter from 2-year-olds, for they are learning that there is an order to the world. Placing a sock on a foot is not funny. Placing it on an ear is hysterical to 2-year-olds because they realize that it does not belong there. They share their mastery of that knowledge through laughter.

Children at that age may also tell you for the first time that they are being silly. Unlike the younger child playing peekaboo, the 2-year-old with the sock has controlled the stimulus for laughter. The child has made a joke.

A 6-year-old child no longer finds peekaboo and socks hanging from ears as funny as they once were. The challenge and the tension of those tasks have been replaced by a newfound appreciation of logic and abstractions. The riddles and jokes of a 6-year-old often contain ludicrous juxtapositions, plays on words, or logical flaws. “Why did the elephant paint her toenails red?” “So she could hide in the strawberry patch.” “What did the baby ghost say to the bully ghost?” “Leave me alone or I’ll tell my mummy!” “What’s the best month for a parade?” “March.” They are simple versions of the humor we enjoy as adults.

The content of these jokes reflects the 6-year-old child’s struggles with the intricacies of logical thought and growing facility with language. The elephant that thinks she will blend into a strawberry patch by taking on one superficial aspect of it does not understand something that the child now understands. It is a funny image to 6-year-olds because they can imagine and identify with the elephant that is trying in vain to hide. The small child knows more than the big elephant. With that knowledge comes power that can be flaunted.

The ghost and parade jokes make use of the child’s increasingly sophisticated skills with language. “Mummy” sounds like “mommy,” but it is not a random association. The baby ghost is calling upon a larger and stronger being for protection, just as the child would. The child has used wordplay to conquer something frightening (a mummy) and transform it into something protective (a mommy). Similarly, the parade joke allows the child to display mastery of the idea that one word can have several meanings. That is a very difficult concept, one that younger children cannot fathom.

The innocent tone of children’s jokes changes before they leave elementary school. For reasons psychologists do not completely understand, by the fourth or fifth grade boys laugh at different things from those that girls do. By the time boys are 10 years old, they are telling jokes that are very physically violent and very sexual. Girls at that age like humor that is less physically but more verbally aggressive, perhaps because they have, on average, better verbal skills than boys. They tease each other about boyfriends and act like caricatures of the vamps they see on television soap operas. The jokes help define membership in a particular social group. Those who get the joke belong to the group; the others are outsiders.

Despite the apparent differences, both boys and girls are using humor to accomplish the same goals. To young adolescents, humor is an indirect way of coming to terms with the issues of greatest concern to them, such as their sexuality. An 11-year-old boy who laughs at a joke about prostitution or abortion is not necessarily making a judgment about either issue. They are far too emotionally stressful for him to deal with directly. Instead, he uses the joke as an opportunity to determine cultural norms and acceptable behavior. It offers him a chance to try out a position and, if necessary, retreat from it quickly, saying, “I was just joking.”