Examples of kidspeak are everywhere, once you start to look. Take our newfangled use of the word because, as seen in sentences such as I believe in climate change because science and You’re reading this article because procrastination. Even 10 years ago, such constructions would have sounded like a clear grammatical error from someone still learning to speak English; today, they have become so widespread that the American Dialect Society crowned because 2013’s Word of the Year. The rhetorical appeal is easy to see: Stripped of its of, because transforms from a way of elucidating one’s case to a puckish refusal to do so. It helps its speaker hide behind the authority of the x—and avoid all the messiness of actual argument. In many ways, it channels the stubbornness of the little boy who asserts nothing more than “Because!” when he’s asked why he scribbled on the wallpaper with a Sharpie.

Or have you noticed that, to convey emphasis or surprise, many young women have begun appending an uh to their sentences? “No-uh!” “Move-uh!” “It’s for you-uh!” Most adults would recognize this as a habit small children typically outgrow by middle school, but women have begun retaining it in adulthood—one can catch it everywhere from the speaking style of the comedian Aubrey Plaza to the local Chipotle. That women have started the trend is unsurprising, as women usually introduce new constructions into a language. Before long, research shows, men tend to catch on.

Then there are exclamations like I’ve had all the illnesses!, which one delightfully droll student of mine recently told me after I asked why she’d missed class; another student told me that his father, a veteran bird-watcher, has seen “all the birds.” This phrasing dates back to a 2010 comic strip by the artist Allie Brosh, in which her character seeks, with ingenuous ambition and little result, to clean “all the things!” It reflects the cutely narrow view of the child who recounts to us specificities of her life, assuming that we, as adults, must be already knowledgeable about them: “At the park, we were doing the jump game and Michael told us we couldn’t take turns until the Juicy Loops were gone!” (What’s the jump game? The Juicy whats? And who’s Michael?)

Clearly, kidspeak affords its users certain rhetorical advantages—the way it playfully softens blows is part of why younger people on social media now often couch what they say to one another in the toddler-esque. But what made bright teenagers and 20-somethings start imitating 5-year-olds in the first place? And why are many older Americans following suit?

The slang of earlier decades offers some clues. The 1920s gave rise to the bee’s knees, know your onions, and be yourself! (meaning “calm down”)—phrases that were less childish than jaunty, cocky, pert. The 1930s and ’40s brought “hep” slang like reet for “right” and chops for “ability.” In the 1990s, veggies jumped from the lips of mothers spoon-feeding their infants to the menus of pricey organic restaurants.