If you have a Kindle Fire and kindergarteners, Amazon is currently rolling out an update for you. Firmware version 6.3.1 is heading to devices as we speak and brings extra parental controls with it. Now, parents can enable a password on purchases to prevent accidental money drains, block specific content libraries, so your kids don't see your naughty books, and even disable the Silk browser so your children don't discover the internet at large. This alone will save you thousands in psychiatric bills.
It's a small update, but if you have little ones, it's important. Especially since tablets and ereaders are more often shared devices. If you have a Kindle Fire, the update should be headed to you shortly, so be prepared.