Why do people in their 20s act like children these days?

Looking at people lately, it's not just those in their early 20s, but even those in their mid-to-late 20s are treated like the youngest members in society or their family communities.
They act cute and childish, belong to the so-called "kidult" culture, or even show signs of regression like playing games like "cops and robbers"—why is this happening?
Is it because they are constantly told they are young that they actually believe they are children?