To limit the amount of negative content traffic while offering positive supervision, set your computer up in a high traffic area like the family room or kitchen. This way, you build in an automatic system of accountability for you and your children. Of course, parental supervision should yield guidelines that teach kids to be responsible for their own behavior. Establish time limits. Too much time at the computer can be dangerous.
Schoolwork can suffer.
When you were young, your parents taught you to never talk to strangers. The same holds true when it comes to online time. Kids are easy prey. Use a software blocker. Your local computer store can provide you with one of the many programs that control and limit access to certain areas of the Internet.