As someone who also worked fast food the second I could and not because I had to, they had very explicit rules about what I could and couldn't do.

I wasn't allowed to even step foot into the kitchen area because it had knives but most importantly, two large spinning blades to shred meat and hot stoves.

The problem isn't children working, the problem is allowing children to risk their body when they might not understand or appreciate the risk they are in with those machines.