The Blacklists pane works the same as the Whitelists one, except it forbids your children from ever accessing the sites listed there. As in the other panes, click the plus button to add sites and the minus button to delete them. Make sure you check the box next to “Use Blacklist” to activate the list. Why are blacklists useful in addition to whitelists? Here's a few examples:

• You want to block your child from checking their webmail.
• You want to block a site or page that offends your personal beliefes or morals but would fall within the included whitelist.
• You want to allow access to all of a site except one page.