We did two classes with about 20 students each. In both our offered courses we had balanced proportions of gender. Age ranged between 16 and 20 years.

We did a questionnaire at the end and got pretty good feedback! About every student enjoyed having been there. A couple of students said that they would have liked to get to know more about the internals of the game and also about how to program in general. We also raised interest in our course of studies.

Do you think this could be used with kids at the age of 7-12 as well or will it be to complex?

That was the age group we originally had in mind. We guessed that it would work out fine :)

Most of the time was spent doing the exercises. We had a couple of rounds where students competed. I'd guess the last 15 minutes went into doing the competition.