I don't have kids yet but for those of you who do, I came across this free application called IMSafer. The application monitors the instant messenger conversations of your children (currently works with ICQ, AOL and Yahoo! Chat) to help you balance protecting your children and respecting their privacy.
The IMSafer service will notify you via email when your child is engaged in a potentially dangerous conversation on IM. As a parent you won't be invading your child's privacy because the software only lets you see a snippet of the conversation that contains the suspicious part of the chat.
To sign up for the FREE service go to IMSafer