Steps
1. Settings -> Accounts -> Family & other users.
2. Click on Add a family member
1. Settings -> Accounts -> Family & other users.
2. Click on Add a family member
3. In the next screen, Click "Add a child" and give email id, if they have one. If the don't have one you can set up one.
4. Click next and confirm in the next page.
5. An invitation will be sent to their mail id. Accept the invitation
6. If you have successfully setup you will see the below screen.
7. Click on manage family settings online.
8. It will take you to the below page.
9. Click on Turn On blocking.
10. By scrolling down the above section, you'll get the option to allow or block specific websites.
11. Similarly you have options for Block Apps and games, set Screen time.