Obviously the parents didn't want them to work in dangerous jobs but for them it was a matter of life or death. They needed money to survive otherwise they wouldn't have the essentials like food, water and shelter.
Child labour was accepted in these times and they didn't care that children didn't get any education, got injured or even died due to harsh conditions.
I hope this answers your question - the bit in bold is the main info but i have included some background to help your understanding.
