Hi, I'm one of the developers of the kid lockdown app mentioned earlier in the thread (
Kids Place). Right now the app allows you to create a safe area on your Kindle (or other Android device) which restricts your child to only those apps you have set up. It has some other features like preventing the child from answering the phone and auto restart of apps so you don't need to be bothered restarting them if you have really young ones.
We are constantly looking to improve the app so if you have some suggestions I'm all ears! Thanks
Bob Riley