Teaching Primary School Students Programming?

NotesSensei asks: "Recently I was teasing the teacher who runs the computer club in my sons' primary school: 'You teach the kids only how to use software but not how to make software.' Today I got an email: 'OK, you're in: teach them programming.' Now I wonder what language should I pick? My first lesson will be the board game c-jump, but after that? The contestants are: Kids programming language KPL (ab VB.net derivate; Java using BlueJ; Greenfoot (and the BlueJ); and HTML. Does it sound like I'm on the right track or should I try something completely different? We are looking at primary 3-5 (that's 10-13 in this part of the world). Where can I find inspiration for the curriculum?"