TALK TO YOUR CHILDREN ABOUT INTERNET SAFETY.
Children need supervision when using the Internet whether they are five years old or 15 years old. When they're younger, you can simply say that you would like to use the Internet together. This can even be a family bonding experience. As they get older, you should express more specific concerns for their safety. While they may not like the idea of your "spying" on them, many will realize that you have to take some precautions for their own good. This is not to say that you have to look over their shoulders constantly while they are online, but you want to make sure that they are not sharing photos or personal information with strangers or putting this information on websites where people they don't know, and therefore shouldn't trust, can see them.