Ask HN: Ideas for exploring computing with youth 11-13?

Last week, I spent some time with about 10 youth, aged 11-13, just answering questions about being a programmer, and a couple different areas of the software industry.

They've expressed desire in doing a little more to explore programming and computers.

I'm looking for any good ideas on how to spend 60-70 minutes with them giving them a brief/light/fun/positive/enlightening experience wit computing.

I know some kids like to do hour of code or Kahn academy, but I'm looking for an idea that is more group related and doesn't require everyone to have their own computer.

One thing I've toyed with is some simple cryptography stuff where we demonstrate with very simplified public key encryption stuff, do some of the math by hand with secrets they want to share with each other, and maybe a little python on a projector to take it up a notch. But any ideas/experiences are welcome.