Sorry, I was a bit to harsh in my initial comment. Your knowledge is good.
But the idea that mainlanders were abused by the locals isn’t historically accurate.
The opposite was more true, to the extent it happened.
I didn’t say they were abused. I said they were resented.
Yes, the poor islanders suffered brutality during the first decades of Japanese colonial rule starting 1895, then again subjected to a new and brutalized/brutal regime after WWII whose opening decades were no fun at all. It’s no wonder they resented their new overlords.
The kids born not so long after? Well, we know how kids can be. If the parents resent the new outlanders, the kids sense it and ... the outlander kids aren’t liked and feel alienated. It wasn’t the kids’ fault, they probably were confused by it all, but it was what it was.