One of the biggest mistakes that most Windows XP users make is to always login as an administrator. (And by most, I mean 99%.) That basically means that you, and any other piece of software running, have unresticted access to the entire computer. It also means that your children are probably using the same account and can install whatever software they want and do whatever they want.
Windows Vista has a couple of features to help address these issues. First, Vista has User Account Control (UAC) which means that even when logged in as an administrator, Windows runs as a normal user and when it needs to do something limited to an Admin, it will prompt you for permission to continue. Vista also makes it easier to run as a standard user. Well, that may not be so much of Vista’s doing and more that software makers now must make it easier or else UAC dialogs will annoy the user.
For the typical home user with children one of the most compelling features will be the built in Parental Controls. You can setup a standard user account for your kids and enable the parental controls for that account. It can filter their internet content that they look at and block things you don’t want them to be able to access like mature content, pornography, drugs, hatespeech, and weapons. (That right there would have gotten this page blocked.) Its a similar concept to a V-chip in your TV, which you should give a try as well. Its pretty configurable too and lets you customize the categories that it filters for and lets you allow specific sites. I couldn’t resist giving it a test and I have to say that it works pretty well. Some pages it will block completely and other pages it will just block part of the content. Just like UAC, when something is blocked, you have the option to ask the administrator for permission and the Admin can enter their password and allow the content. The parental controls include activity reports of the websites the user accessed (including which ones were blocked). The activity reports are pretty comprehensive and will even show you account logins, failed logins, instant messaging activity, and more. You can also specify which programs they can use and you can limit games based on their rating. I think it really will enable parents to keep their kids safe, which is a concern for a lot of parents.