Does each of your kids ahve their own login account on the computer, do you all share one, etc? If they all have their own accounts, then you can go in and give them permissions. Set them up as users that can only access certain software. That way they couldn't get on and just use Kazaa to download porn and such. Make them as you to "allow" them to use it by doing a "Run As" on the application, and loggin in under the administrative account. That way you know when they are on it and such.

Another thing would be to use the security settings under "Internet Options". The "Content" tab will allow you to restrict access to certain sites. Sure it's not the best thing, but it's easy.

Also with anything you use a password on, try using different passwords for different things. Like one password for your admin account, one password for the Content in Internet Options, etc. That way incase they do find out the password, they can't get into everything

Also create yourself another account, that you never use, which has administrative rights. Try to hide it, just incase they might get into your administrative account and change the login password. Then you still have a sort of back door into the system.

Use a key logger, that's a good idea. The only thing I don't like about that is, they can use it on you too if they know anything about computers, or might be watching what you area up to. REmember kids these days are getting better with computers.

That's all I can think of off the top of my head right now, will post when I think of more.