Maybe require all apps to have a built in spending limit and an affirmative act per app to raise it with a mandatory password prompt and click on an emailed link to verify.

Make it up to $50 one time or greater than $100 in one calendar month. Given how people actually spend 99% of people will never see such a prompt and virtually everyone that hits it will be one of these people who is being scammed out of their money inadvertently by their kids.

While we are at it we could simply ban all games designed to appeal to the scratch ticket mentality and nothing of value will have been lost.