Safe Search is a tool provided by Google that eliminates sexually explicit content from Google search results. Google support states,
When SafeSearch is on, sexually explicit video and images will be filtered from Google Search result pages, along with results that might link to explicit content. When SafeSearch is off, we'll provide the most relevant results for your search and may include explicit content when you search for it.
To enable Google Safe Search
Select the family member that you would like to enable Google Safe Search for.
Tap Filter in their profile settings.
Scroll to the bottom of the filter options to the Privacy & Safety toggles. Turn the Google Safe Search toggle ON (to the right).
NOTE: When Google Safe Search is enabled on a family member's profile, access to Bing and Yahoo Search will be disabled. Access to sites such as msn.com or yahoo.com will still be available.
IMPORTANT: Circle only enforces the use of Google Safe Search and does not control the effectiveness of the tool directly. If you run into issues with how Google Safe Search handles particular search terms, please contact Google support to let them know where the tool is failing.