I'm afraid of my children when they online there are so many bad thing going on, how to control them and know which web-page they access...

Here is some FREEWARE software that can filter out bad sites..
K9 Web Protection - Free Internet Filtering and Parental Controls Software

Blue Coat® K9 Web Protection is a content filtering solution for your home computer. Its job is to provide you with a family-safe Internet experience, where YOU control the Internet content that enters your home. K9 Web Protection implements the same enterprise-class Web filtering technology used by Blue Coat's Fortune 500 customers around the world, wrapped in simple, friendly, and reliable software for your Windows 2000, Windows XP or Windows Vista computer.

Blue Coat's unique Web filtering technology divides Internet content into 60 distinct categories. These categories are stored in the master Blue Coat database, through which we maintain and update more than 15 million ratings of websites and domains. A Web site will fall into one or more of these categories, based on the content of the site. To meet your particular needs and preferences, you can configure the software to block or allow specific categories.


K9 Web Protection is different from other solutions for the home in several important respects:

* Service-based filtering – Blue Coat's filtering database operates as a service. It receives and rates over 80 million requests every day, making it the most accurate content filtering database available. This accuracy is important in protecting your family, given the Internet's rapid changes and growth. Plus, there is no database to download. K9 Web Protection won't clog your Internet connection, get "stale" or out of date, or slow down your computer like other products do.
* Dynamic Real-Time Rating™ (DRTR) – Blue Coat's patent-pending DRTR technology is a very powerful element in our solution, and is vastly different from the old-fashioned "key word filtering" that is so frustrating to users. Using a method of statistical analysis and artificial intelligence to rate new or previously unrated Web pages, DRTR can determine the category of a URL on the fly, without human intervention. However, DRTR only renders a rating when it is confident that it has reached an accurate conclusion.

We've focused DRTR on recognizing the kinds of categories most likely to be blocked. In particular, DRTR is highly accurate in blocking pornography and other "adult content" sites. This focus for DRTR is particularly important because these kinds of sites are constantly – daily and even hourly – popping up on the Internet, and no static database can keep up.
* Automatic updating – Automatic updates of the K9 Web Protection application ensure that you are always protected by the latest features. For example, in Spring of 2005, we added two new categories to our solution: Spyware/Malware Sources, and Spyware Effects/Privacy Concerns. By electing to block sites in these categories, your computer's rate of infection by unwanted software can be reduced dramatically. We have a variety of new features planned, and your K9 installation will automatically receive updates that include them.
* Efficient caching – K9 Web Protection is a product from Blue Coat. Blue Coat is recognized world-wide as expert in high-performance caching and secure proxy technology. We take advantage of that expertise in K9, so your Internet experience is as fast, reliable, and safe as we can make it.

Unlike other filtering solutions, K9 Web Protection ensures the highest level of protection by building the most relevant ratings database available. Its effective coverage reaches more than one billion Web pages. With K9 Web Protection, you finally have a chance to build a family-safe Internet experience for your home, simply and easily.

I believe u can block all the sites except cartoon network and stuff just to be sure... also you can install some programs to monitor all internet activity, including yahoo messenger.