While legislation was passed pre-WWI sort of forbidding child labor in theory or establishing 8-hour work days, what many corporations tended to do for next couple of decades was instead of hiring pre-teens and young children, mining, timber corporations started hiring workers in their early teens like 13-15, a bit older in age from 8-9 year olds in the 1880's and 90's in the "Gilded Age" but still flirting around in that grey moral area legally and sometimes even breaking it. And many industrialized workers in essential sectors still pulled 14-18 hour days well into the 1930's and Great Depression even during WWII.