I absolutely hate anything inside of a kids app that gives my kid the opportunity to buy, install, or even view anything I haven't vetted. Ads are especially bad.

I like the idea of a buy button that makes you prove you're an adult by typing xyz in a box, or some other trivial-for-an-adult task, before it launches the store. IIRC Zoodles' "Kid Mode" has a voice that says "ask an adult to help you with this" any time a kid tries to access a premium feature.