Ask HN: Pointers for designing a programming club curriculum

I am planning on starting an after school programming club and my children's school, initally targeting grades 5 - 8 (ages 10 - 14). Some assumptions I currently making:

     - The club would meet either once or twice per week for an hour for the entire school year.
     - Expected attendance between 5 and 10 kids.
     - I will be providing / directing purchase of hardware, and am imagining purchasing 10 Raspberry Pi's along with monitors and keyboards.

The goal of the club is to introduce these kids to programming, and I"m looking for a project or series of projects that could be worked on over the course of the year to help build interest in programming.

I want to reinvent the wheel as little as possible and am asking if anyone has suggestions for curriculum for this sort of club. Possibilities I've thought briefly about so far: some sort of game (though I have not experience in developing games) and building websites that we gradually make more sophisticated (this is more up my alley).

I'm asking for pointers to help me develop a curriculum. If you've done something like this before, I'd love to hear what sort of wins and challenges you experienced as well.

Thanks in advance!