Said the latter, regardless of religious beliefs, a program like DanGuardian (http://www.dansguardian.org/) can filter undesirable material for children and anyone else using that computer system (sorry adults, no porn for you after the kids go to bed). This application can be installed and configured on "Linux, FreeBSD, OpenBSD, NetBSD, Mac OS X, Solaris or HP-UX" (http://www.dansguardian.org/?page=requirements).
Then again, you can also get it pre-configured in Ubuntu Christian Edition (http://www.ubuntuce.com/), which is basically an Ubuntu (http://www.ubuntu.com/) installation with DanGuardian and Bible study software like Xiphos (http://www.xiphos.org/), which I use.

Needless to say (type), DanGuardian is also available pre-configured in other variations of Ubuntu for other religions like Judaism and Islam.
By the way, these are my comments about DanGuardian and not an advertising. Of course, if the folks at DanGuardian want to give me some money, I'll gladly accept it.