I have a 4 year old, a 1 year old and an iPhone. Therefore I am at risk for unwanted App Store purchases. To combat this I can do one of two things: 1. disable the App Store completely or 2. force the App Store ask me for my Apple password before each purchase.
Option number 1 is not really an option but rather a lock down of one if the major selling points of the phone. Option number 2 is more manageable.
Here are the simple steps to help save you time and money.
Step 1: go to Settings
Step 2: go to General
Step 3: go to Restrictions
Step 4: go to Require Password and change from 15 Minutes to Immediately
Note on step 3, if you have not setup a 4 digit pin, you will be asked to do so. Make the pin something you easily remember as you will need this pin to change or set any restrictions going forward.