That's odd, the article I read did contain specific instances of parents retracting the steps of their spendthrifty offspring which confirmed there was no indication of actual money being spent, e.g.:

“I saw all these $19 charges from Facebook,” she said. “It added up to nearly $1,000.”

She asked her son why he would do that. But he was flabbergasted by the charges too. So Bohannon asked her son to play the game so she could watch what he was doing wrong.

As he played, he occasionally clicked on a corner of the screen that gave him more abilities, such as magical items, or new ninja attacks for his character. It didn’t ask if he wanted to pay for it, or let him know that his mom’s credit card was being charged.

“There was no indication he was spending money,” Bohannon said. “So, 20 minutes later, I rechecked my credit card statement online. And sure enough, there was another $19.99 charge from Facebook.”

Holy cow, that's frightening. Mobile games with in-app payments are clear about "These cost gems {or some other bought-with-real-money mcguffin)", but refilling those gems nearly always makes it clear that you're going to have to pay.

Facebook payments platform was always far behind Apple & Google Play in terms of transparency.

Source documents are linked throughout the story.