1. From Ubuntu top Menu click on Aplications / Accessories / Terminal.
2. Install firestarter:
sudo apt-get install firestarter3. Close the Terminal Window and click on the top Menu System / Administration / Firestarter. At the end of the Wizard check "Save" so the Firestarter program Window appears.
4. Click on Policy tab.
5. Select from Editing "Outbound Traffic Policy".
6. Check "Restrictive by Default, whitelist traffic"
7. Right click on the box below "Allow connections to host" header.
8. Select "Add Rule" from the contextual menu.
9. Insert for example "gamesgames.com" (without quotes) in the box named "IP, host, network".
10. Click on "Add" button. Click on "Apply Policy button".
11. Your kid can just visit http://gamesgames.com. But you see some images are missing on the site. When you inspect the source of the image (right click on top of the image showing up there and click on properties from the contextual menu to see the URL) you notice it comes from www11.gamesgames.com. So just go ahead and add it to the rules as explained before and get back to the URL.
There is a little work involved here every time you want to open new URLs for your kid. But you would agree with me it is simply worth it.
Very important, do not share with him/her your root password so access to Rules policies cannot be easily changed.