Unfortunately the interest in sex has hit my daughterr's second grade class already. She came home a few weeks ago and asked why boys were saying 'sex me' to girls.
After talking with other moms at the school, I got more information than I expected about games girls and boys have been playing since 1st grade. Fortunately my daughter was not in class last year with the main kids who seem the most fascinated with sex, but we talked about not playing games that feel uncomfortable after I learned what is going on.
I have spoken with the school counselor and she was well aware of what is going on and said they are handling it, but then yesterday my daughter said one boy said he was 'hot in his pants' for girls and was going to go 'relax with his girlfriend' and proceeded to make out with his hand. He got written up but that doesn't seem to make any difference.
In speaking with a friend whose son goes to school in south Texas, I learned this is not just happening in my daughter's school. I don't remember this stuff coming up until I was in 5th grade so I was caught off-guard. I think kids are being exposed to sex at an earlier age through various forms of media and aren't really aware of what it is so they just repeat what they see and hear.
I think counseling would be a wise idea....help him understand what is going on and try to avoid addictions and sneaky behavior that could lead to other things later.
Also, I build websites for a living and have never allowed my daughter to go online on her own. I don't leave the computer on and she does not know the password. She gets computer lessons at school so she knows how to use it, but I have never encouraged her to spend time online. The only time she gets online is when I am sitting with her to Skype her aunts. I don't see the value in exposing kids to computers at such a young age other than getting some basic understanding at school. I would lock down your computer so you son doesn't spend time on it. Find other things to keep him occupied so it doesn't feel like a big deal that the computer time is going away.