This will only work with younger kids but they are the ones I am most worried about. Also this is with the intent that this is a seperate device.

Set up a different account in Amazon for your kids to use. Use an email address on this account that you don't normally use or create a new one. (I use the gmail account thats attached to my Android phone)

Name this is Amazon as your child's first name. (So the Fire says your kids name in the corner)

Set up this account on the Fire

Every time an App or Book is downloaded (free or pay) an email is sent by Amazon to this email account. You get to see what they have purchased.

Add only Kindle gift cards to this account if you want them to be able to make purchases. No credit card is ever needed.

The Fire already has the ability to password protect in App purchases.

Please add any other suggestions or thoughts. Sorry if you think this was already self explanatory