A common complaint among tablet owners is the lack of safety measures to block unauthorized users from buying content. Nevemind thieves; it turns out that kids and meddling coworkers are a bigger issue. There have been any number of stories of kids running up bills for hundred of dollars in in-game content on their parents' account, and the froth in the blogosphere got so loud that even Apple realized that adding password protects was a good idea.
And today Amazon adds a feature that really should have shipped on the KF. This update brings additional parental controls to Kindle Fire, including the ability to password-protect purchases, disable access to specific content libraries, and block access to the Silk web browser.
You can simply wait for the update to be pushed out to your Kindle Fire, but if you want it now you can download it here.