Earlier quoted context omitted.
The definition of the length of the work week and who it applies to is already a concept defined by government.
Stated this way it makes it sound as if the government, unbidden by anything external, just decided to make this a requirement one day. Of course, this was not the case. In reality workers, unions and even industry leaders themselves were already pushing for this decades before the government codified it in the Fair Labor Standards Act.
When child labour was legal, lots of children worked.