Menace Decay

Times change, and the standard for what constitutes a troublesome kid changes with them. A child character who was once considered to be quite the hell raiser can appear completely tame after a few years. Ironically, the longer the menacing kid is Not Allowed to Grow Up, the more likely he is to become his exact opposite, an impossibly idealized version of what the author thinks a child is supposed to be, due in part to authors' habit of modeling such characters after their own real-life children. The alternative is trying to preserve the character's reputation as a hellraiser through ever-escalating Flanderization. In either case, it's not going to resemble the behavior of an actual child, because, of course, Most Writers Are Adults.

See also: Values Dissonance, Motive Decay, Villain Decay. Often occurs when the child is Not Allowed to Grow Up.

Comic Books

 * Your Mileage May Vary but some fans consider the Dennis the Menace reboot in 2009 when the new TV series began to air on CBBC turned the character from a menace into just a generic kid.
 * Inversely, Dennis's rival Walter the Softie has changed into more of a Jerkass over the years, making him less sympathetic and more of a deserving victim.

Film

 * Played with to some degree in the The Little Rascals movie, in which the kids are basically the same despite the fact that the setting is about 70 years later.
 * The 1971 Willy Wonka and The Chocolate Factory movie. The kids are bratty, certainly, but by today's standards don't really deserve all the perils they're put in. This trope is also probably why the kids in the recent adaption were made much, much more intolerable.
 * Though they never really deserved what they got, it was classic Roald Dahl over-the-top parody of morality tales.
 * Although what they got was from cause and effect, in the same way jumping into a lion's cage will get you mauled.
 * And they all got better.

Literature

 * By 1960 standards, Scout, narrator of To Kill a Mockingbird was a classic tomboy. Read the book from a modern point of view, and you can only tell she's not supposed to be a feminine girl because people keep saying so.
 * A reader can see this in between the generations in the two different Petaybee trilogies- Murel and Ronan get into far more mischief than any of the "troublemakers" in the first series.

Newspaper Comics

 * The Trope Namer is the American Dennis The Menace, who has gone from being a genuine terror to being a perpetrator of minor, almost exclusively-unseen mischief. Consequently, Mr. Wilson's grudge against him has gone from sympathetic to downright petty, as the only thing Dennis ever does to him anymore is barge into the Wilsons' house from time to time and ask Mrs. Wilson for cookies.
 * Modern-day Dennis has occasionally gone even further into the realm of Family Circus-esque Glurge, as seen in panels like this. In an ironic twist, in that particular panel it is now this very thing that annoys Mr. Wilson so much.
 * This trend and its causes are further discussed here.
 * Observation of this phenomenon is also a running gag in the comic-commentary blog The Comics Curmudgeon.
 * This occurred with Bil Keane's The Family Circus. As the title suggests, the kids (who were based on his own) were originally written as wild and hard to control, but it has long since fallen into the realm of Tastes Like Diabetes.

Western Animation

 * The Simpsons: Bart Simpson is a perfect example of the flip side of this trope--his Kick the Dog moments become more frequent in order to keep his reputation as a hellraiser. He's not Eric Cartman yet, but is definitely pushing the envelope on the 'comedic' part of Comedic Sociopathy. Almost starting a war with Australia, burning down a camp, etc.. Preserves his reputation but at the cost of sympathy.
 * Lampshaded in an episode where they go to the beach and the local slacker townies make fun of his iconic skateboard and sling shot, outright comparing him to Dennis the Menace. Also lampshaded when he met Jay North, who played Dennis in the 1959 TV series. Bart wasn't impressed by "bad boy" antics such as stealing Mr. Wilson's hat.
 * In one episode of South Park, Eric Cartman meets a Bart Simpson stand-in, and they compare their evil deeds. Bart brags that he once sawed the head off a statue (but felt bad about it afterward.) Cartman, on the other hand, killed Scott Tenorman's parents, ground them into chili, and fed them to him.
 * This is likely a response to a bit in the Simpsons where Bart compares his deeds to Dennis the Menace with similar results. In one episode Bart was called "this century's Dennis the Menace." And the episode aired in the 20th century.
 * Eric Cartman is again what you get when you avert this trope. Moral Event Horizon aside, most of his actions are either Poke the Poodle or Politically-Incorrect Villain moments, even moreso than Bart Simpson. But said Moral Event Horizon was so intense that no amount of Menace Decay will ever really redeem him.