It's a sad and confusing story about ancient business.
The mama-san offers money to underage girls for sexual actions.
I'm very sure the young girls knew what they had to do. And they did it voluntarily for money.
Who is to blame?
The girls for greediness or the parents neglecting their children or at least not knowing what they do/where the money came from.
These 3 have been "rescued". However, now the know how to earn money when they are 18.
Many university girls/men offer sex for money.
So not surprising.