I think there's a line somewhere and for me the line is whether the job is suitable for children. Like, doing chores around the house or on your grandparents' farm. Paper route riding a bike. I worked summers at a carnival, and at a pool when I was a bit older. Low physical labor, low responsibility, low customer interaction, family friendly environments. You're right it should never interfere with education.

If I saw a kid at the register of a fast food place or a store, I would turn around immediately and never return. Just leaves a bad taste in one's mouth.