Function of Preventing accidental or unauthorized purchases (Recommended for parents)
You can help prevent accidental or unauthorized purchases on your iPhone, iPad, or iPod touch, by setting Restrictions.
After you turn Restrictions on, a password will be required for in-app purchases.
Thus, it is highly recommended that parents set Restrictions to block unauthorized in-app purchases made by your child(ren) or third parties.
Please refer to Apple Support for the detail of the procudure of Restrictions setting through the following URLs:
Thank you for your understanding.