I've done this in Chicago. You didn't specify their ages, I'm assuming these are high-school kids. The important point to stress, I think, is that computers and programs are all around us, and not just as computers, either. Ask them to name a computer they use daily, then surprise them with the usage in dishwashers, cars, etc. (these are more microcontrollers but the distinction is not important).

From there you can go to the theme of "be a programmer of be programmed", i.e. everybody needs to know some coding. Tell them that math is not a prerequisite (a usual worry about programming) and show them some cool but simple game programming examples using Scratch, pygame and the like. In fact, it would be great if you can create a game during the presentation, with ~10 lines of code.