I looked at a free one from CloudMark, called SpamNet. This product is currently in beta development, and I evaluated beta versions 3 and 4. I noticed that they currently have a Beta version 5b available. The design was interesting (all web based), but I did not like the lack of user configuration (by design), and it also locked up Outlook XP on me several times. But you may like it, especially for the price --- free!
Another product is actually marketed under two names:
What I like about this product is that:
They have versions that work with Oulook, Outlook Express and AOL
It works as an add in to Outlook, meaning it's running when Outlook is running
You can set it so that the Spam never appears (go for your children), but you can always review mail that has been quarantined
Products can be currently purchased for $19.95.