According o developmental psychologist Paige Davis, who specializes in socio-cognitive development and imagination, the main element needed for humor to evolve in children is socialisation.

"Children must understand that they are sharing an experience with another person before they can begin to establish a sense of humor," Davis wrote.

"We typically do this by laughing and sharing reactions together – a process that effectively starts as soon as a newborn can engage in eye contact and smiling."

However, a child needs to possess a few basic cognitive skills to communicate the jokes we see in the pictures (beyond just pulling a funny face).

The most important ones are imagination, the ability to take a different perspective, and language.

Because these abilities tend to develop at different rates in different kids – and continue to grow and change throughout adolescence and adulthood – there is no firm theory that can pinpoint specific, age-related stages of humor development.

"Infants without language and younger children with limited language typically enjoy physical humor, such as a game of peek-a-boo," Davis explained. "But such simple jokes, involving less cognitive skills than language-based jokes, are also about incongruity realization. Peek-a-boo has an element of surprise – someone suddenly appearing out of nowhere."

"Indeed, many researchers argue that it is communication that is key – and that humor actually facilitates the process of learning a language."