There are ways to have content filtering for free that will protect anyone who connects to the Internet from your house, without the need to install any software on their computer. It is a system called DNS filtering and here is how it works:
Every web page out there has an underlying TCP/IP address. That address is the unique identifier of the server that is hosting the content, and it looks like http://nnn.nnn.nnn.nnn where nnn is any number from 1 to 255. In order to find the page, the URL you are looking for, let's say higbyfamily.com, gets sent to a Dynamic Name Server (DNS) that matches the name higbyfamily.com with the unique TCP/IP address of the server, which in this case is 184.108.40.206. Consider that higbyfamily.com is the name of the site you want to access, but that 220.127.116.11 is the Internet "Phone number" of the site. Without that phone number, you can't connect to the site.
That is how DNS filtering works. Consider that the DNS service that you use is the Internet phonebook. If you wanted to prevent access to certain sites, all you have to do is cross out the phone numbers and replace them with:
I'm sorry, the number you have dialed is disconnected. Have a nice day!
There are a number of free services that help you do just that. I have used both http://dyn.com/dns/ and opendns.com. These two services have their own DNS servers which you can reference from your network instead of using the default servers that come with your Internet provider. You use their internet phone book, so to speak, instead of the unrestricted phone book. Each service provides a web panel that allows you to specify what kinds of sites you want to block on your network. You can reconfigure this as often as you want--say, block game sites during school days, but open them up on the weekend.
To get this system working for an individual computer is simple, but not very effective. You can edit the network settings for one computer and manually add in the address for the DNS servers. However, the minute these parameters are set back to the default, the Internet filtering will no longer be in effect. It is far better to change these parameters inside your ADSL or cable modem or router. Instructions on how to do this vary for your specific router model, but if you look up the manual on the Internet, you should be able to find instructions on how to change the DNS server on your network to use the addresses provided by either of the above two services.
One last note. These services rely on knowing the specific TCP/IP address for your home network. Without that, they cannot provide individualized filtering for your specific preferences. The problem is that many Internet providers do not give your home network a fixed address, but the address changes dynamically several times a day. You can find out if you have a fixed address or not by googling "what is my IP address" and taking note of the resulting number. Restart your router and look up the number again to see if it has changed. Check again a few hours later. If your number has not changed, then you are blessed with a fixed IP address and filtering will work without a hitch. If your number does change, then you need to follow extra steps below.
A changing number is called a dynamic IP address. There are two ways to get around this. The first way and by far the better way is if your router web administration panel has a section called dynamic DNS. If it does, it most likely will provide a way for you to connect with dyndns.com to update your IP address every time it changes. You would then use dyndns.com as your filtering service.
If it is not possible for your router to update your IP address automatically, then you would be better off using opendns.com. They provide a utility that runs on one of the computers on your network and will update your IP address to the openDNS servers every time it changes. You would want to use the computer on your network that is on most of the time. That being said, the first option is so much better that you should consider upgrading your router to a more sophisticated model that includes the ability to automatically update your IP address. I am currently using the Thomson ST780WL which has very nice features. The ST585 also allows updating.
No Web filtering is perfect, but the goal is to reduce the obvious temptation. I remember standing with my mother in the checkout aisle at the grocery store in watching as she flipped several of the magazines in the display rack around so that the cover was no longer visible. Anybody could still get to them if they wanted to, but the temptation to stare at them was removed. These content filters not only protect against pornography, but they also protect against known phishing sites, and even have a setting to block advertisements if you so wish. I love having this protection on my home network. Any computer that comes in the door, is automatically subject to the rules of the household -- without installing any extra software. Pretty cool!