Install a program on your computer NetPolice. It exists in both free and paid versions. There is a version for the Linux operating system. Select in the program settings, resources what kind of subjects your child cannot view.
To not install on the machine any software, use the online service of the same service NetPolice: set as primary DNS server the IP address 126.96.36.199, as a secondary - address 188.8.131.52. To implement this in any OS. Will be filtered requests to the sites of the category "Pornography".
The disadvantage of programs that are installed directly on the computer, and reconfigure DNS, is the ability to bypass these measures, for example, when booting from the Live CD (the children are inventive, and reset the BIOS password for them nothing). Much better to make filtering the content of the pages was carried out by the provider. In this case, it would not have to reconfigure your baby equipment, to obtain access to dangerous websites, he can not. For information about the availability of this service, please contact support at your ISP or cellular operator. In the second case, you can limit the access of the child to dangerous sites and mobile phone.
Some providers this service is implemented in some other way. Filtration is carried out not by the content of the pages, and on time. The child will be able to access the Internet only during certain hours, and all you have to do is watch those around him and monitor what resources it sees.
Note, however, that even safe the Internet can be used as "babysitters" for the child, as was the TV. Communicate more with him, and when he uses the Internet, could tell him the interesting sites the subjects that interests him. Themselves engage him in particular, and using the Internet, say, sports, arts, technical creativity.