If you're looking for a fun browser-based tool for managing your kids' access to the net, you might want to give Glubble a try. It's geared toward the younger set (under 12, I'd say), and is super easy to use. It's also FREE. And we all know, I like FREE. The kids are even enjoying it as it gives them each a slick front-end for browsing and accessing kid-friendly sites. It's an add-on for Firefox, so installation is a breeze. Each family member gets a customized browser and there's even a "family wall" for leaving each other messages. If you child encounters a site they cannot access, but want to, an auto-prompt appears to send a message to you requesting that you add (or not add) the site to their approved list. So far, it's one of the least intrusive tools we've tried and has actually led to the kids discovering some cool new sites.
Here's a link, in case you're interested: