I am hesitant to even write this post, for fear of generating some curiosity. The only reason I do is because your content filter will probably not automatically block this site - and you will want to keep your children away. Please, take my word for it, and add these two URLs to your block list: ChatRoulette.com and ChatRT.com.
This is a relatively new site that is catching on very quickly. According to this post, it grew from 300 users in December to 10,000 in February of this year. The site allows you to randomly connect via video chat (that is, through the webcam on your computer to the webcam on another computer) to another individual who happens to be using the site at the same time. If you don't like who you are chatting with, you click "next" and are randomly connected to another person.
You do not want your children accessing this site. If you have a content filter installed, add this to your block list. If you don't, now would be a great time to install one - before your kids stumble across it.