DuckduckGo has this by default.I suggest you to try enabling Safesearch on your browser. Just open Google in a browser and go to the Google preferences screen. By activating SafeSearch, you can filter explicit search results in Google Chrome and other browsers. Also, try using FamilyShield for blocking porn and related adult content. Hope it will help you.
neustar dns is enough for me
But k9, sophos, forticlient have free ones