I wouldn't have a problem with a kid of mine "working in fields", provided the hours are reasonable. Picking strawberries, outside, with friends their same age, a few hours at a time, would be great for them. I would go as far to say that its fun.
I would prefer that over them having to interact with a bunch of asshole strangers, alone, trapped inside all day.
No problem if it's the family farm, or a trusted neighbor's. Plenty of kids grow up raising their own pigs and growing carrots and whatnot.
Hell no if it's paid employment on some stranger's farm, or an industrial feedlot.
Reasonable hours is something that goes without saying. Study, chores, play, work - in that order - is how kids should be taught to prioritize their time. They're your children, not your free labor.
Not sure where I grew up has anything to do with it other than that my examples didn't take into account some rural edge cases (family farms constitute a tiny sliver of all farming). The context of the work, and how dangerous it is, is what's important.
I don't mind my kids doing the former at a young age. The latter - hell no.