Things that seemed to work well:
1) Find a basic computer game with available source code and have them play it for maybe 10-15 minutes to understand the game.
2) Teach them a basic Hello World type of app in the same programming language as the game.
3) Open up the games source code and start looking for any sections that seem "readable" in the sense of lines that can be manipulated to affect game play (eg: # of lives for a character, response of actions, speed of play, # of enemies, etc.). Walk through some basic edits, re-compiles (if required) so that they see the impact of code changes on a larger project. This is, IME, more rewarding to a limited attention span audience than starting from scratch.
4) Come up with a simple coding project than can be modularized. Assign 1 student or group different subroutine tasks and then pull it all together into a larger program that runs each subroutine. Simple ideas are things like a conversion app utility, expense tracker, etc.