I would go with what I wish I had known first: a simple MS-DOS box and the integrated assembler (debug). It is great to really learn and understand the basics of talking to a computer.
If that does not scare away a child, then I would go the "next level up" and introduce C. This shouldn't be hard given that the basic concept of pointers, registers and instructions in general are well-understood by then.
However, I am not entirely sure, where to go next. Take the big jump to Lisp, Haskell or similarly abstracted languages or should there be some simple object oriented languages (maybe even C++) be thrown in or would that more hurt than help?
