Kidult

The portmanteau coinages kidult, rejuvenile, adultescent refer to adults with interests traditionally seen as suitable for children. A kidult is also a person who claims to be a kid at heart, whilst endulging in forms of media meant for children, or a person who shows signs of Peter Pan syndrome. It can also mean a parent who acts childish with their children, but does not take on their duties as a disciplinarian. 
An example of the word in popular culture is Robin Williams' character in "Mrs. Doubtfire", a father who has fun with his children but is a poor disciplinarian and is seen by his wife as an irresponsible head of the household.
In the past, psychology recognized the concept of "puer aeternus", or "eternal boy". Today, often called "Peter Pan syndrome", it means a person remaining emotionally at that of a teenager or even a child. It is derived from the traditional archetypal "eternal boy", Peter Pan.
One of the most well-known and extreme cases of Peter Pan syndrome and the kidult mentality is Michael Jackson. Michael had explicitly stated that he did not want to grow up and he also said that he owned an impressive collection of arcade video games, toy cars and fantasy and sci-fi memorabilia. He also had a fascination with Peter Pan’s character and one of his dreams, never accomplished, was to create a theme park called “Neverland Ranch”.
In the early 21st century, there was a sudden increase in reporting that for an adult to have interests traditionally expected only from children is not necessarily an anomaly. This is mostly due to the rise of the entertainment industry. The entertainment industry was quick to recognize the trend, and introduced a special category, "kidult", of things marketable for kids and adults alike. Enormous successes of films such as "Shrek" and "Harry Potter", of animated television series such as "" the target demographic of young girls, of young adult fiction books traditionally targeted for teenagers and the fact that Disneyland is among the world's top adult (without kids) vacation destinations seem to indicate that "kidulthood" is a rather mainstream phenomenon. Kidlthood also appears to exist on the Internet, with grown adults treating each other like children, especially in political discussion on Twitter, by calling people "homegirl", "girlie", and "sweetie". And unlike "puer aeternus", "rejuveniles" successfully marries adult responsibilities with non-adult interests. When Christopher Noxon appeared on "The Colbert Report" on June 29, 2006, he remarked that "There's a big difference between childish and childlike".
Karen Brooks has wrote about what she calls the "commodification of youth": entertainers sell "the teen spirit" to adults who in the past were called "young at heart".
In South Korea, the buzzword "kideolteu" was used in 2015, highlighting the market trend of increasing toy sales (such as drones and "electric wheels") to adults.
History.
The term was first used in April 1, 1963 in the academic journal "Sociological Inquiry", Volumes 33–34, on page 189, when it was describing escape methods used in recreational programs for children, kidults, and adults. 
The term was also used in 1982 by Jim Ward-Nichols on the campus of Stevens Institute of Technology in Hoboken, New Jersey, in its campus humor magazine "DUCKLIPS". It first appeared in the mainstream media ("The New York Times") on August 11, 1985 in an article by Peter Martin. 
It was used in 2006 by Kate Crawford in the book "Adult Themes: Rewriting the Rules of Adulthood", and in 2008 in the book "Anytime Playdate: Inside the Preschool Entertainment Boom, or, How Television Became My Baby's Best Friend".