When I was 9, my mom remarried to a man who had two daughters - 6 and 8yo. They were only with us for holidays.
Every Christmas (for 8+ years), I would receive 2-3 practical presents (a coat and shoes for example) while they would open up 10-15 fun presents each in front of me. I told my mom that she should have taken me on a walk or elsewhere so I wouldn't have to see them opening presents while I got very little.
She said I should have understood that we were struggling and not been so immature about it.