I like the idea of the second monitor a lot. Something that i just did with my son's computer is to install parental control. I asked him to give me the websites that he likes to go and i added them to a web list. He can only go to this websites and this parental control recognizes him as a young teen and blocks information and advertisments that are not recommended for his age.
Comcast provides Macfee for free and the parental control is included. Great tool to make sure your kid is protected from information that is not appropiate for his age.