For the 6 to 10 years old boys and girls, we have done a Scratch workshop.
Scratch is awesome, it has all the basics of programming: blocks, loops, conditions, events, event sharing, etc…
Here, not need to prepare much, explain the basics and let the kids go (see below).
For the 10+ kids, we have done the Arduino workshop: programming electronics for the win :)
We have reused the Devoxx4Kids one verbatim.
We were also lucky to have the Aldebaran team with us.
So the kids moved up from the basics of programming to full Nao robot programming.
Nao is a serious guest start and actually easier to program than Scratch :)