Parental controls are a great way to lock based on ratings, or to lock content available for purchase.  To activate Parental Controls, visit your Settings page by selecting the Settings tab or by selecting the gear icon, then select Parental controls.  Start by selecting Enable.

Settings Screen Parental Controls 

Next, you'll be prompted to create a PIN number. Make sure it's unique and secure.

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Lock content based on rating by simply checking the appropriate box. Select the Lock Purchases box to lock movie rentals or other content available for purchase.

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Any content that fits the rating criteria will appear with a faded thumbnail and lock icon. 

If you'd like to watch a locked show or movie, you'll be required to enter your parental controls PIN to unlock the content. After entering your PIN, your selection will begin streaming. If you forget your PIN, select Pin Reminder to reset your PIN. Depending on your device, this may also display as Forgot PIN? Forgot Passcode? or another option.

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You can also set and manage your Parental Controls settings from your My Account page.

Go to My Account >