@Plykiya probably because you didnt look... as almost every kid..
i remember girls in my class in 5th grade also not cared about not showing panties, but i also didnt checked them, because i just played with others classmates that time, but now when i walk around kids on park, or even play with my niece, she too not care, she even play naked, i also once put pajamas on her, when she refused to go sleep.
kids are just innocent (normally) to care about this, because they not know