Pinker's discussion of child labor in Enlightenment Now is pretty good, but the best part is his reporting on an advertisement for a farm tractor in 1921 that was pitched around the idea that buying a tractor would enable farmers to keep their boys in school during the spring plowing season. "Keep the boy in school - and let a Case Kerosene Tractor take his place in the field. You'll never regret either investment." [Note the language of human capital "investment" here too!]
This is, of course, just the male version of the washing machine, which enabled girls to go to school rather than spend one day a week at home helping with the family laundry.
Apparently you can get books out of both a washing machine and a tractor.