If a three year old came into your hardware store waving his mother's credit card and assured the staff that he had parental permission to buy a chainsaw, would you fire the employee that sold him that chainsaw? Or would you, like the company in question in this article, refuse to respond to phone calls from that confused mother?
They aren't using a card though, at least not directly. They are playing a game.
It sounds like many games are set up to 1) encourage you to enter account information at some point and 2) not make it obvious when you are going to spend more "real" money.
Obviously these situations could be avoided in various ways, but I think it's being pretty hard on parents of young kids to blame them entirely for "falling for" scenarios that are pretty dodgy. Especially if you are a) a technologist of some sort and b) don't have kids, I would really think carefully before deciding the parents are 100% at fault.
I do have kids, and make abundantly sure that any payments on my kids' devices go through Play / App store (not a card directly), and always require a password. It does not require technical knowledge; both systems clearly show relevant controls at every purchase.
I see how being a parent of a young and active kid can be exasperating. But, if anything, it should increase the level of healthy paranoia :)
Much like a three-years-old should not have an ability to light matches, or push a screwdriver into a power socket, or operate a chainsaw.