Seems hard to imagine it's beneficial for the kids other than in situations where there are fewer germs outside but as cultural idiosyncracies go it makes a lot more sense to me than the fear of sleeping with a running fan in Korea.

In Germany there's an obsession with stale air in rooms, during the day you "auslueft" the room but when you're in the room you close the windows and doors to prevent uncomfortable or even unhealthy drafts.

Irrational health beliefs are very stubborn, like many Germans my mom and her sisters believe that sitting on a cold surface can lead to bladder infections, here in the US nobody seems to know about this.