If Amazon's updates cause resetting of in-app purchase flags, learn to deal with it. Part of dealing with it is to inform Amazon that their policy is broken, but it's their policy to make; if you don't like it, move on to the next or learn how to deal with it to fit your needs.
No, it's not their policy to make. You may wish it was, but (1) that's your individual opinion, (2) that's not the law, and (3) there are quite a number of people who disagree with you which, even in a representative democracy, goes quite a way to ensuring that your opinion is unlikely to become the law.
Quite a number of states, alongside the FTC, have laws governing unfair and deceptive trade practices. They've had them for quite a long time. Your ultralibertarian viewpoint does not reflect the way the world works, or apprecitate the difficulty even above-average customers have in finding good information about how a product or service actually works before purchasing it, or consider that 'learning to deal with it' or 'moving on to the next' have substantial after-the-fact costs, or actually demonstrate why we should permit a practice like 'resetting in-app purchase flags' on a routine basis.
You're perfectly happy assigning responsibility to the parents, yet you're willing to give the manufacturer/service provider a complete pass even after parents have learned the technology they use, and used the very mechanism provided by the manufacturer/service provider to deny the ability to make such purchases, only to see their efforts actively thwarted by manufacturer once they are 'on the hook'? It makes no sense.
Although we warn people 'caveat eamptor,' we do not endorse that as an absolute governing principle of business. You can neither intentionally design in nor conceal a material product defect, whether its a lock mechanism in a car or a parental control in an app store, and expect the public to say "well we just have to learn how to deal." Once you design in that sort of mechanism, it has to actually work as a reasonable person would expect it to. Otherwise, you become liable under any governing philosophy, whether it's Austrian school laissez-faire capitalism or European-style consumer protection regulation.