There are two Parental Control systems that co-exist on the Xbox.
Xbox Family Settings
If you use the Xbox Family Settings to control which movies and TV shows can be watched through Xbox LIVE, the Quickflix app will follow these settings. For example, if you prohibit watching of M-rated programs on your console, those programs will be marked with a 'restricted video' icon in the Quickflix app. To play a locked item, an adult must enter the Family Settings pass code.
Quickflix Parental Controls
If you have activated the Quickflix Parental Control system via the Quickflix website, the Xbox app will require you to enter your Quickflix Parental Control PIN.
If you have both systems activated you will be required to enter two PINs for restricted content. If your PINs are different for the Xbox and Quickflix systems, be sure to enter the correct PIN in the corresponding fields.