Disable no admin access to terminal?

I am the admin on my macbook pro and i'm running 10.9.2.
I have another user that I would like to disable access to the terminal. I believe you can do this rather easily through parental controls but I'd rather not have that alert pop up. My son uses this computer and is somehow disabling my kernal based logKext program that I have installed as when I log in using sudo it comes up as ttys000 after he uses it with no log. He doesn't have my admin password, nor admin access, but I believe he is logging in as root though sudo commands. If anyone can offer any insight...

(disclaimer: I'm not a parent)

I think he's demonstrating that he's a pretty bright kid, but not ready to be given responsibility to use a computer unsupervised yet. That he's aware you have a logging program and knows how to disable it would equal no more computer time on your machine I should think.

(also he'd have to know an admin account password in order to run as root, so your assumption that he doesn't know your password may be incorrect)