Sounds like you really put some thought in that lesson, sounds really fun. I used to run a gaming company and our players were around that age. Here's what we dealt with most:
Maybe you could give an example of brute forcing insecure passwords and how simple it is to hack your accounts with insecure passwords.
Maybe you could give an example of a keylogger that is installed via an email attachment or java web applet. Most examples of this i saw using a youtube video advertising "cheats" for a game if they install something but really it was just a keylogger or a RAT.
Maybe you could give an example of session hijacking (for example their Facebook session.
Maybe you could show how easy it is to make a copy of a website and send somebody to it to steal their password. For examppeexample what we saw a lot is youtube videos claiming that you can get free stuff on a website only if you entered your password.. obviously they stole the stuff :-) you could do this by making a post on a forum that accepts HTML input in posts and adding something like
<a href="http://facebook.login.example.com">Log In To Facebook</a>
Lastly, maybe you can put something about the exposure of yourself when you add somebody on Skype (IP address, maybe location etc).
Hope that helps!