Recent surveys report that 71 percent of teens and 34 percent of 11- and 12-year-olds have a profile on a social-networking site like MySpace or Facebook.

Even if your kid knows that he's not supposed to post private information online, there are some common silly mistakes that may expose him to bullying, identity theft, and other potentially negative consequences at school and, later on, in his work life.

Mistake 1: Overlooking the privacy settings

MySpace and Facebook recently improved their privacy practice, giving users much better tools for controlling who sees what:

• If your child is setting up a page for the first time, sit with him and look at the privacy settings. Experts advise using the strictest privacy settings from the start.
• If your child already has an online profile, check to see if it's public by Googling his name or searching for him on Facebook or MySpace. You can do this together. Also Google a friend or two of his, to compare and contrast. It's an occasion for you to talk about what the right values for your family are.

Sometimes teens share passwords because of peer pressure:

• Teach your child to pick a password someone can't easily guess.
• Talk to your child about the importance of not sharing passwords under any circumstances.
• Keep an eye on her pages for clues that someone else violated them.
• Punish her if she breaks the rules. Experts suggest punishing your child offline — not allowing her to attend a friend's party, for example — rather than banning her from a social-networking site.

Mistake 3: Adding strangers to their friend list

Teens accumulate friends on Facebook or MySpace because it makes them feel popular:

• If your child is new to social-networking sites, establish a rule that you must approve all friend requests, just like you would approve who she brings into your house.
• Friends should only be people your child knows personally.
• Click around their friends list occasionally.

Kids open up too much and post a lot about their personal lives online. They share an intimacy of conversation that they would never have with those people in real life.

• Emphasize to your child that too much sharing online can leave them open to bullying, mockery, and social isolation.
• Tell them that anytime they put something on Facebook, it's like shouting it with a microphone in the middle of the school.

Mistake 5: Looking under their feet

A study published in the Archives of Pediatrics & Adolescent Medicine showed that 54 percent of 18-year-olds on MySpace post about behavior such as sexual activity or substance use. Posting about these adventures can hurt them in the college admissions and future job searches:

• The best protection is not to post any explicit material in the first place.
• Formulate a story about how if your kid posts a picture and then deletes it, anybody can copy it when it's live and come back to haunt him later.
• Check their pages -and their friends' pages- and don't give up talking about online safety.