And if “don’t be rude to teenagers over a stupid jawbreaker” isn’t enough for you, consider
You can’t tell how old a kid is just by looking. I’ve known multiple 5th graders who were taller than I am, and I’m 25 years old. With their faces hidden by masks, you won’t be able to tell they’re elementary schoolers, but they still are.
Lots of older siblings are expected to take their younger siblings trick-or-treating, and they only get paid in candy.
You don’t know if that teenager is developmentally disabled.
You don’t know if that teenager spent most of their childhood in a hospital or sick and has never had the traditional trick-or-treat experience before.
You don’t know if this is that teenager’s first Halloween in America, and they just want to experience a piece of American culture.
You don’t know if that teenager ever gets candy any other day of the year.
You don’t know if that teenager has eaten anything at all today.
And those are just things I can think of off the top of my head.