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 examppe 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 :-)

Hope that helps!