That's only for people with Google Apps for Education (teachers)!! Also, if you are under 13 you can't use the site if you didn't sign up with google/facebook (which have their own weird under 13 rules)
EDIT: Also, I found out that youtube actually doesn't let anyone under 13 use their service, so I'm guessing you can't watch the videos either if you're under 13. See "12. Ability to Accept Terms of Service" in (http://www.youtube.com/static?gl=US&template=terms)
I just found out the internet is just for people over 13...
See "1. Eligibility" in (http://www.khanacademy.org/about/tos)
EDIT: Also, I found out that youtube actually doesn't let anyone under 13 use their service, so I'm guessing you can't watch the videos either if you're under 13. See "12. Ability to Accept Terms of Service" in (http://www.youtube.com/static?gl=US&template=terms)
I just found out the internet is just for people over 13...