First, before you ever turn the computer on, you should explain to them how computers work from a high-level that a kid can understand - i.e. how they are dumb, and they just follow instructions that we give them, and how those instructions are what's known as the program, etc.
Then I would suggest starting out with Hello World in Javascript. Javascript is straightforward, relatively forgiving, and it's on every computer, so it's basically the modern-day BASIC in my opinion. Show them what happens when things go wrong, not just when things go right, in order to drive home how computers are really just slaves to our directions.
Then maybe have them start working on a game, one piece at a time. Kids like games, after all. Maybe something simple like Tic-Tac-Toe or a Pong clone. The main advantage here in using Javascript is that they can email it to themselves and then play it anywhere with no need to set anything up - they can also continue to tinker with it on any computer after the teaching is over.
Then I would suggest starting out with Hello World in Javascript. Javascript is straightforward, relatively forgiving, and it's on every computer, so it's basically the modern-day BASIC in my opinion. Show them what happens when things go wrong, not just when things go right, in order to drive home how computers are really just slaves to our directions.
Then maybe have them start working on a game, one piece at a time. Kids like games, after all. Maybe something simple like Tic-Tac-Toe or a Pong clone. The main advantage here in using Javascript is that they can email it to themselves and then play it anywhere with no need to set anything up - they can also continue to tinker with it on any computer after the teaching is over.