I was in the food court at Costco when I spotted a boy about 12 years old, carrying a piece of pizza that he'd just bought. It fell off his skimpy plate and onto the soiled tile floor. He was embarrassed and a bit miffed with himself and went to throw it away. I told him that he should take the pizza back to where he paid for it and they'd probably give him another one.
He looked at me a little out of sorts and that's exactly how I would have felt at that age
--not assertive in the least. Then the boy's mom walked over, looking a bit disappointed, and I told her the same thing I suggested to him. He came back with a new, clean (unless you count the grease and cholesterol) hunk of food and she thanked me.