Quick and easy intro to computer science for kids for an Engineering Field Day
Since Logo was intended for this age group you might explore something there. My quick idea would require two or three screens with some sophisticated and time consuming simulation running on one and the kids/adults exploring simpler exercises that might (or not) build up to the one running. You can run, for example, a space filler (Sierpinski) program and have the students explore turning, etc. With lots of trial and mostly error. 

In Karel J Robot, the recursive graphical solution to the Eight Queens problem takes a bit of time and is built up from only a few primitives that can be combined and extended. So that would do for the running demo and the students can explore simpler aspects, such as a robot backing up, for example. The advantage of Eight Queens is that it is easy to explain, unlike, say, sorting. 

You can do this sort of thing in most languages - a complex graphic simulation built up from simple parts. The students explore only a bit of it. They can even modify some of the code of the running sim and run it to see what happens. It can lead to a lot of laughter, and some insight. If you sit with them you can suggest things that do something fun/weird/good/bad and ask why that happened. Lots of possibilities. 

But the running sim gives an unattainable target in the time frame. Like playing on the beach after professional teams of sand-castle builders have shown their skill. 



The suggestion is that if the simulation is built with something like Model-View-Controller that the students only modify parts of the model.