Support / Settings overview / Blocking / Force safe search for YouTube

You can prevent inappropriate content from appearing in YouTube search results by enabling restricted mode. You can enable this in your Google account settings, in the search settings of a particular device, and also at the network level so that all devices on your network will be locked to restricted mode regardless of Google account or individual device settings.

To enforce restricted mode for your whole network go to safe search in the Category section under Blocking in your account settings.

Choose between moderate and strict
You may want to enable SafeSearch for Google searches as well for good measure

Screenshot showing settings for enabling or disabling Safe Search

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