My parents would buy me $10 of gaming stuff as a kid, like a month subscription to an MMO. Seems unreasonable to expect them to know there's some in-game button I can press that keeps charging their card. I played World of Warcraft for five years and still couldn't tell you if that feature existed in-game. How would my mother?
Seems like a tall order especially with all the other things a parent needs to stay on top of when raising kids. "Just don't make digital purchases" seems like a weak solution. Small measures like having to re-enter the CC control code after a time interval would really help parents.
The pattern is very simple. If the game has an in-app purchase along the lines of:
* Buy 10 gems: $0.99
* Buy 50 gems: $2.99
etc. then it's F2P garbage. Get rid of it. Take the five minutes to see what your kid is playing.
Otherwise, you're asking to ban these games altogether or make them 18+. All because it's too much trouble to see what they're actually doing with that iPad you throw in front of them.
Like have a default maximum spend in Facebook of $5 per app and $50 total, and require at least a double-lock to enable a higher level of payments.
Double lock: user confirms by ticking a box and by following a link in an email, say; then they get a message on their Facebook saying "you authorised higher spending for $game, up to $amount".
They could require pre-deposit, not allow use of credit cards, only allow spending if your credit rating is good, etc.. But none of this things increase mindless spending.
So, stop right here. The solution is for parents to take a look at what their kids are playing and refuse to let them play F2P stuff. Mine aren't allowed anywhere near F2P games for the very reasons you outlined.
If you let them play F2P games, you know that inevitably the "pay" part is going to rear its ugly head repeatedly, even with perfectly-implemented controls that prevent the kid from taking your credit card for a ride. Every damn day they're going to ask you to buy that stupid in-game currency. Just say no before it ever starts. Otherwise, good luck.