It's generally agreed that some of the charges for "In-App purchases" on iPads and iPhones are excessive. Some would even describe it as daylight robbery!
These apps are normally "Free" to download and use but pretty quickly you're asked to buy more coins/tokens/fairy-dust to progress, often these are aimed at children.
Here's how to disable In-App purchases in iOS 7. If you're still using iOS 6 you should still be able to use this guide, it'll just look a bit different.
1. Choose System Preferences from your phones screen
2. Click on General
3. Click on Restrictions
4. Click Enable Restrictions
5. It'll ask you to enter a passcode twice. it's important that this passcode isn't the same one as you use to lock your phone as, chances are you'll need to give the restricted person the code to unlock your phone to play the game anyway.
6. In the initial list is an item named In-App Purchases. To disallow In-App Purchases this should NOT be green. The default is that it's allowed so you'll need to click it.
That's it. Click the home button and that'll be saved. Now when someone is offered an In-App purchase on your phone they'll get the following message