One of the cool unsung new features of iOS 6 is the way it doesn’t ask you for a password every single time you go to make an app purchase. The downside of this convenience is the in-app purchases is kinds of out of your control now.
Hop into your Settings app, then tap on General. Scroll down to the Restrictions area, and tap into it. Enable Restrictions with a tap on that button at the top, there, and enter a Restrictions Passcode. This can be totally different than your Lock Screen password, if you have clever kids. You’ll be asked to enter the passcode twice, to make sure it’s one you can type in twice in a row the same way.
Scroll down to the Allowed Content area, and find Require Password. Tap on it and set it to Immediately. That way, no matter what, your iPhone or iPad or iPod touch will always ask for a password when any in-app or app purchase is requested, by you or anyone else. You lose a bit of ease, here, but it just might be worth it to avoid paying too much for something you don't want at all.