Aren't there quite good DNS filters (like what OpenDNS provides) for the worst parts of the internet? You don't want them looking at porn, gore, extreme politic

Aren't there quite good DNS filters (like what OpenDNS provides) for the worst parts of the internet? You don't want them looking at porn, gore, extreme politics, social media, self-destructive behaviours, drugs, and at particular sites -- that kind of stuff, right? A DNS filter sounds like a better tool for this than time restrictions with all that content available for 1 hour a day or whatever.