Start-->Run this command (replace http://www.e3girls.com with site you want block) :
echo 216.239.51.100 [url]www.e3girls.com[/url] >> C:\WINDOWS\system32\drivers\etc\hosts
Repeat as needed. This may not work immediately if you just visited the site, but certainly will after reboot. May not work against smart kid though :D
And always double check that you have two ">" symbols, not one.