The Cuties' and Sweety Swags' origins of sexual precociousness may have no In-Universe explanation, however when you consider that these girls have social media accounts, namely Instagram, it's more than obvious that they're being exposed to and influenced by the many viral youth dance trends popular on TikTok and similar platforms, which very much include twerking.
For a universe where underage sexual behavior is rampant, Police Are Useless is played as straight as you can get, seeing as how there are venue posters advertising the girls' twerking group. But if that's not enough, no legal action is taken on-screen when a video surfaces of the Sweety Swags (who are implied to be under 18 given their attendance of public school) with one of the members flashing her bare breasts on-screen, or when Amy posts a photo of her genitalia online. In fact the girls just barely avoid being called the police on when they're let off the hook by the security guards after proving they're a twerking squad.
