How to change your iTunes password interval with parental controls on your iPhone or iPad

[iMore.com]

By default the App Store and iTunes only requires a password every fifteen minutes or so. That means if you've authorized a single purchase, someone could technically purchase something else without being required to enter a password again. For parents who want to prevent this from happening, you can easily use restrictions in order to require a password be entered for purchases immediately and every single time.

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