[iMore.com]

Many apps and games in the App Store offer in-app purchases, which let you buy additional content or levels inside the app. The problem with in-app purchases is that they can be quite expensive, especially inside games. There have been several horror stories of parents receiving huge credit card bills due to small children racking up in-app purchases. If you don't ever want to be in the same boat, you can easily disable in-app purchases so your kids can't buy anything inside apps that they don't have permission to purchase in the first place.

Full story from the iMore Blog...