I started with BASIC programs written on my TI-86 to automate math problems; they may find that a useful way to get started, and learning a little BASIC shouldn't be much more brain-damaging than learning Javascript.

I kind of have a problem with training people to "code" rather than teaching computer science; feels sorta like comparing a "wine and painting night" to a course in oil painting, in that you might shortcut to something acceptable-looking but with little understanding of how or why you did it. But they're kids and will probably quickly tune out during Dad Explains Linked Lists :)

Ideally I'd suggest starting off with some smaller guided exercises to get them familiar with the language, then work with them to spec out and implement a more interesting project. In my CS courses in college we implemented the minimax algorithm for tic-tac-toe and checkers, starting with a tic-tac-toe engine which just printed out its desired move and evolving along until we were displaying a checkerboard as it played along. Could be a good project for you since it's implementing something they're familiar with (board games), doesn't use anything weird like networking, and can introduce concepts such as recursion and complexity ("if we have it calculate the next move, how many possible moves are there? What if we calculate the next two moves? The next three?")