Parental controls can allow and block access to certain types of websites to protect vulnerable persons and children from accessing content, voluntarily or not. It is also often used for business who wish to ensure that use of professional equipment is kept for professional use only.

Parental controls only work on the MVNO mobile network – not on WiFi.
Parental controls won’t work on iOS devices with iOS 15 or newer when browsing using Safari and for some app traffic when iCloud Private Relay is enabled. 

There are three settings according to the desired level of safety:
Strict – Recommended for kids (under 13)
Moderate – Recommended for teens (13+)
Off – Recommended for adults (18+)

In more detail:

Strict
This setting filters all 18-rated content but also content the BBFC rates higher than ‘PG’ as well as other content not suitable for younger children including chat, dating and unmoderated social networking sites.
Google SafeSearch is now built into the Strict settings, so any Google search will not show websites that relate to unsecure or adult content. You can’t turn this feature off with this setting – you’ll need to switch your parental controls to Moderate or Off.

Moderate
This setting gives access to social networking sites but not to 18-rated content in accordance with BBFC (British Board of Film Classification) guidelines or to pornography sites.

Off
This gives full access to the internet with no filter, including to 18-rated content.

Of course, enabling parental controls is a good way of protecting children from accessing potentially harmful material, but it does not guarantee 100% protection and does not exclude other safety measures such as supervision, open dialogue and scheduled internet times.

Users may want to check with their Internet Service Provider for content settings on their home internet/WiFi network.

Further guides and information can be found here: https://www.internetmatters.org/

On most offers, the default level of data content access is set to strict. You can check with your account manager to be sure.
Otherwise, these may be set automatically when applying a service profile or activating a line via API.
You also have the option to select which level is required upon activating a line via Auriga.

If you try to access 18-rated content with parental controls enabled, you’ll see a blocking page – similar to that if a page couldn’t load.