Mac OS X has had parental controls for a while now. They are similar to parental controls in Windows, if you are familiar with them. The Apple Support page for Parental Controls has the description, “keep your children safe by monitoring the time they spend on the Mac, the websites they visit, and the people they communicate with”. There is video showing how to set up Parental Controls and walks you through the steps.
Time limits are probably the most useful feature, because the other restrictions only work for the standard Mac OS X applications. Most kids will find a way around those other restrictions by using a browser other than Safari, web mail such gmail or hotmail, and by chatting on facebook or Skype. The logging feature does provide parents with a useful history of what the kids have been up to.
But, did you know that you can set up parental controls from another Mac on your network? So, you can change the parental control settings without needing physical access to their Mac. The only catch is that there is some initial setup on the child’s computer. You will need an admin account on their Mac, and it should be an account the kid doesn’t have access to. You will also need to allow remote setup. All the details are available here.
Maybe this all sounds a bit creepy and like you are stalking your children, but if it helps them get enough sleep, by getting them off the computer automatically at a reasonable time of night, its probably worth the complaints you will get. And if you can give them an extra hour to finish that important assignment, without having to venture in to a teenage bedroom, it should make the experience a little more pleasant for everyone