Geek master: It would be a very long time before I could learn enough Linux to be able to do this. And as you said, a child would probably soon be able to "fix" the wifi. But I'd be willing to pay for a program or application that can do this for me. I'm sure there are other parents who if they knew all that a curious kid could do with a Kindle and free wifi access they too would pay for a disabled device, or a way to password the device so that only the parent could access wifi if needed.
I've taken away the cell phone and the laptop, next to go will the be the well loved Kindle 3 until I can solve this problem.