My grandsons,age 8 and 10 at the time were verbally harassed by kids at LAX waiting for a flight.
My guys had Red Sox Tees on and the others had Yankee shirts on.
It’s an on-going rivalry.
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Where I live (in NYS) there are mostly kids with Yankees shirts but quite a few Red Sox fans as well. They usually just joke with each other and what ever team is ahead in the standings is brought up. I have relatives that love the Red Sox and bought my youngest a Red Sox T-shirt when she was 5. She loved it because it was “red”. It was really big so we made it her paint smock at school. :) it came home covered in blue paint!