Updated with some additional warnings:
I noticed a lot of folks bought Kindle Fires for Christmas. If you let the kids use it, please note that they can purchase apps without any password or warning. You can turn off in-app purchases through parental controls (apps>store>settings>parental controls) but you can't disable first-time purchases, no way, no how (unless you completely disable the Kindle from amazon), even if you have already disabled 1-click purchases on your account.
(I find the threat of bodily harm, however, usually does the trick.)
I think it stinks, but my son says it's fair game. These dadgum young, whipper snappers.
(you can remove all credit card information if you don't find adding them for each purchase rather tedious.)
PS I don't mean to be a killjoy if you are loving your new toy, because I am enjoying mine as well, but better you hear it from a friend than to find out the hard way...the Kindle has no parental controls for surfing the Internet which is pretty scary if your kids are free to take it a quiet corner. There are also many pornographic style books available for free (no credit card number or password necessary), and if you are a Prime member, there are lots of free movies, many of which you really don't want the kids to view.
The bottom line is, use with great care and supervision.