Answer:
D. New laws requiring younger children to go to school
Step-by-step explanation:
Factories never had to pay children a fair wage because before the labor movements children were removed from the workforce entirely.
Both B and C have nothing to do with children so that can not be the answer
The only one that is left is D and that is the correct answer. New laws came into power during the first half of the 20th century and many highschools were built at that time.