Taking the UK as an example, legislation restricting the use of children under 14 in employment was only adopted in 1933. Previously it looked more like this: https://en.wikipedia.org/wiki/Child_labour_in_the_British_In...

The USA didn't change things up considerably until the 1930s: https://en.wikipedia.org/wiki/Child_labor_in_the_United_Stat...

Not soon after, obviously ww2 and then the baby boom after that. The role of children in families changed hugely in the 20th century.