Install the policy in knowledge base Enabling SafeSearch for Google search but safe search is not enabled yet.
As most of search engines now use SSL to communicate with the user, SSL interception must be enabled in the proxy SG, so the proxy SG will be able to read the traffic, and add the required headers for safe search as per knowledge article Enabling SafeSearch for Google search.
For more information on how to implement SSL interception please read knowledge article Configure SSL intercept for an explicit deployment using a self-signed certificate.
Some more information on Google Safe Search https://support.google.com/websearch/answer/186669?hl=en