you can’t accept such a stay without parental consent in writing, with a passport copy’of the parents maybe. If airbnb does not want to cancel, I would ask them to confirm, that’host guaranty covers potential liabilities, like the parents demanding child suport if the girl gets pregnant during the stay. Not to mention potential criminal pursuit for prostition of a minor, as the host facilitates the proceedings. In France, they could pursue you for that.
I’m glad they came to their senses on second thought and cancelled the stay.
After a single minor guest on a relative’s passport, I raised the question with a friend who works as a policeman in minor protection. He told me to never accept such a booking, as it can land you in horrible problems. Imagine the minor guest falls ill or has an accident. You have to call an ambulance and then explain, how a hurt minor ended up in your house, no one knows any contact info or real name, nobody can decide on surgery or treatment.