I think that you are idealzing a bit outcomes of children in the past. They had their own set if problems - including higher violence and criminality rates and alcoholism etc.
Violence and crime rates are down due to the reduce use of lead in gasoline. Alcoholism seems to be down due to much greater difficulty in being able to drink (can't drive the bar anymore without fear of stiff penalties) and greater information.
But I don't think I am idealizing anything. The benefits of having a job when you are young are abundantly clear, and remain abundantly clear for those who still do so today. There is no reason why children cannot work and also have pursuits that are useful in other areas. It is not an either-or situation. They do not need to be full-time jobs. There is plenty of time for other pursuits.
I had job as teenager. There was no obvious long term benefit and no short term benefit except a bit money more. It did not harmed me either except being unable to do certain activities I wanted to (which would gabe me more back then, but not more enough to regret it too much).
You can't explain all past farms violence by lead, that explains violence peek in 1990. The past rural situations and societiés in general were not nearly as idyllic as people make them be.
