America has had tons of immigrants working 24/7 to run a restaurant, a laundry shop, or a drugstore, while putting their kids through school. Most of them weren't forced to come to America or choose such a job: they did it because even maintaining a 24-hour convenience store is less grueling work than planting rice, and they're rejecting their children's "help" because they want their children to study and have even better, more comfortable jobs.

Pre-modern agricultural societies had huge families because there was so much work that you could always use an extra pair of hands. (Also, many of them died off anyway so you had to factor that in.) You are looking at the past with a seriously rose-tinted lens.