New (2014) see Monitoring with a Transparent Firewall, for another option in addition to those below.

If you are a parent with a child/teen who use the Internet, there is no reason to not Monitor, Filter, and Block some potential Internet activities. There are free applications available. They are easy to install and easy to operate.

You’ll need to do some reading at the above web sites to discover which application is best for what you are trying to accomplish.

Don’t forget mobile devices! Smart phones and tablets are powerful computers.

Applications for mobile devices are not as available as those for desktop computers, but there are some. The options change too frequently to list them here. Use your devices’ application store to locate these.

Call your cell phone provider, or login to their web site to find what parental controls they offer.