I hope whoever posted this on the Steam forums doesn't mind but they do raise a good point:
Children existing isn't illegal, nor are children being skimpy. The issue is that PSO2 allows you to do things that other games don't that directly violate US law. For example, the laws related to CP include masochism. That means that emotes like the recent KonoSuba one in which your character takes sexual pleasure from being physically beaten by sentient cabbages would violate this law if done on a child character. The laws also include general obscenity.
The most important thing about the law is that it states that these acts merely need to be simulated. Which means that anything sexual or obscene doesn't actually need to happen to the character is question. It would just have to appear that such acts are being done against them. So in other words, these loli characters existing aren't illegal. It's what you can do with them specifically in PSO2 that could violate US law.
Keep in mind that a US court has already charged a person for possessing drawn loli hentai in the US. A legal precedent has been set and the courts ruling has never been undone or challenged. Even Japan is starting to crack down on loli/shota within recent years.
This was debunked in the same thread it was posted in.