How do I disable the Mac App Store?

I have a special needs son and for this reason I have to limit what he has access to on his iMac.
With the Mac App Store coming I had made the choice to simply not install/download the Mac App Store. I realized that this morning that is not an option, it is installed as part of the 10.6.6 update.
I removed it from the dock but still I realize it is installed on the Mac and for example it's an option on the Apple pulldown menu and I know there is an option of when a file cannot be opened there is an option to open the app store to find an app.
I looked at Parental controls but unless I am wrong could not find an option to completely disable the app store. I don't mind enabling it when I want to install certain apps on his mac that he will need. This may be convenient but simply don't want him to be able to get into the app store to install apps.
Thank you for your help.

Parental Controls will let you limit access to applications but only lets you set which applications one can use (you can't say which ones you don't want someone to use, you have to say which ones are okay to use). See here. Does this work?