Another vote for OpenDNS.
You can choose to use their FamilyShield option which is free, or pay an annual subscription of 10$ and select your own filters. Familyshield is not infallible, there were reports of RedTube being accessible a couple of years ago.
The benefit of a premium membership is that you can also view the domains that have been accessed over a given period:-
You can then look at individual domains:-
You can see which domains have been blocked:-
If any domains get through that you don't like, then you can block them (this takes 3 minutes to upload to all servers) and then refer the domain for review.
Finally, you can customise your settings so that the internet access is exactly how you want it:-
Obviously, the DNS settings are applied to your router and then your router secured so that DNS settings cannot be altered.
If you use a dynamic IP, then you can also install software that updates the IP if it should change.
OpenDNS also prevents access to Phishing websites automatically.
Hope this helps
