Starting from iOS 4.3 when you make your first in-app purchase it will ask you for a password and any further purchase for next 15 minutes will not require you to enter password any more. So the only way to make sure your kid is not taking advantage of the 15 minutes frame is that you need to sign out from the App Store Account. This is good but there is a better way to do it :
- Open Settings on your iPad / iPhone / iPod
- Go to General > Restrictions.
- Tap on Enable Restrictions, add a password which you only know.
- Look for a section which says Allowed Content
- First setting in that is In-App Purchase, Turn it off. ( By default it’s turned off, just make sure it is )
Done this two things are sure, One nobody will be able to make an in-app purchase and second nobody can enable this unless you know the password. Now when somebody tries to make an in-app purchase, this is what it will look like : ( A message is displayed which says “in-app purchases are not allowed” )