Legally the parents consented to the charges, but it’s clear from the leaked documents Facebook knew parents thought it was a one time charge not something their kid could spend without limits.
But the complaint here is that the headline implies that it means something that they used the term whale. It doesn't.
Whales are just a segment of customer. And incidentally, there are real, legit whales. There are a lot of rich people in the world who willingly throw money at luxury items like exotic cars, expensive vacations, lavish parties, etc. And some of those people like to play video games too and are totally content spending $500 or $5,000 on coins and junk for a game.
Basically there are two ways to interpret this story. One of them has Facebook salivating while asking themselves, "Is this kid a whale?" The other interpretation has Facebook asking themselves with some degree of concern, "Is this whale a kid?"