I say unusual in the sense of Japan seems to be the only one to have solved the issue of how do you transport 2 kids on a bike not with "big box" like the dutch and subsequently the entire western world but via 2 seats, they're apparently very popular over there as a means of transportation.
used to cycle to uni years ago, almost entirely along a protected, 2 lane cycle path. Still managed to take a corner at the bottom of a hill that I'd do every day wrong and fully Looney Toons myself head-first into a tree, would've been concussed at best if it wasn't for my helmet. Accidents happen, inconvenience of carrying a helmet around is worth keeping your precious brainmeat safe