[Nippom]

This was inspired by the 'No gaijin allowed' thread, but seemed just unique enough to merit its own thread:

Reading some of the replies in the 'No gaijin allowed' thread, I just happened to remember the classic American scene where a group of boys will create a makeshift 'club house' and post a crude cardboard sign that reads 'no girls allowed'.
This is often made fun of, or variously glorified by some artists seeking to give 'color' to Americana, or vilified by some amateur social activist types with their own agenda.
It may not be so acceptable today, when little kids are reputedly shut down and told more frequently by real police officers that 5-cent or 25-cent street-side lemonade stands are against the law, and the PC (politically correct) movement tries to see evil behind every perceived social deviancy.
To be fair, I would venture to guess that girls are equally as likely -or unlikely to- do this, perhaps in less-open ways, in sometimes excluding boys.

This is all speculation and allegation, not stated fact, so there is no need to come down on me like a ton of bricks for the above, but it has been known to happen and I don't speak either if favor for or against, but only voice my curiosity.

Do young Japanese girls or boys ever do this kind of thing, and if so, how do they show or demonstrate it socially?

Some boys and girls -up to puberty, whether singly or in groups- can sometimes tend to view members of the opposite sex as being virtually from another planet.

I wish to differentiate between this kind of 'boys vs. girls' group mentality, as opposed to school age bullying.
I'm not asking about bullying, which is a completely different subject.