I'd take a different approach. Just make a simple game in html and edit it in front of them to add features, change the size of the monster, ... Wait a minute, it's 2025, probably use Kotlin or React to show the game in a tablet.

tell them they're making lots of sandwiches and they can work together in a line or they can work in parallel

I think one obvious approach would be to assign "roles" - one person is "operations" and is the only one allowed to read the instructions to you, one person is "research" and has access to the list of ingredients, etc. But that probably bottlenecks things too hard and you have to figure out a fast way to assign roles. You could just increase the difficulty by requiring more precise instructions? Ah, you split the list of instructions into four parts and put one list in each corner of the classroom, then randomly sort people into the corners - one corner has ingredients, one corner has operations, one corner has conditionals, one corner has goals, and the class has to communicate to build valid instructions. Maybe give the ingredients tongue-twister names and make them devise ways to communicate without getting things confused. And obviously the end of the demo is "so why didn't any of you just take a list of ingredients and walk over to the list of operations so you didn't have to shout?".

This is too weird. Think about something more hands on and practical.

Sorry for the digression, but there was an old Soviet children's book about programming called "Encyclopedia of Professor Fortran" that almost had your jelly example -- except that in the book it was peeling potatoes instead of spreading jelly.

Shaggy dog story: when I was 9 my teacher assigned us homework that entailed writing an instructional essay on how to make the infamous PB&J sandwich. At the time I was a budding "programmer" and had recently seen a skit on a TV show that employed hijinks similar to

> * I brought a serrated knife and ketchup packets. When they said put the jelly on the bread with the knife, I gripped the serrated end and pretended my fingers bled (ketchup works great as blood).

> * I brought in vaseline AKA petroleum jelly. When they said put jelly on the bread, I contemplated aloud "Well, you said JELLY, and this says JELLY!"

...and so went into great prescriptive detail about exactly how I'd make said sandwich. After turning it in my teacher chose my essay specifically to repro onto a transparency and place on the overhead as an example of bad writing. Apparently being explicit about choice of ingredients, removing things from packaging, holding the bread, etc. was antithetical to the assignment and dismissed with laughter and eye rolls because "everybody knows" to do these things.

This was a bit of a blow to my fragile ego but in retrospect it was an important lesson in several concepts that you touch on later in your post such as good communication (the importance of considering one's audience), asking clarifying questions (because requirements are hard), and interactions with authority figures.

I say all of this to say that you should absolutely emphasize this less technical side of things. Soft skills are at least as important as technical aptitude when it comes to career mobility and emphasizing them early would give students a real leg up. While considering edge cases and assumptions is clearly important for computers it's also crucial to keep in mind how people understand processes and systems, i.e. when to be explicit and when to avoid patronizing those on the other end of your comms.

I think the sandwich demo is really good. Once you establish the sandwich idea you can start zooming out to OK now you have a cook making multiple sandwiches, now you have a whole kitchen, and use that to talk about levels of abstraction and how SWEs go from solving one specific problem to more general problems by reusing techniques

What about something about prompt engineering?

Just a callout to Logo.

https://en.wikipedia.org/wiki/Logo_(programming_language)

You might consider some of the pre made stuff at https://www.csunplugged.org/en/

Scratch is a popular way to teach kids programming. It’s very basic but easy for kids to understand and many can do very complex things with it (someone made a super Mario brothers clone).

One of my kids picked up scratch immediately and did that for a couple of years for fun and now he’s doing python and machine learning.

Oddly enough, my mom taught computer programming at a community college in the early 80s, and she used the PB&J lesson, though without physically making one. She also used to remind her students: "Computers are stupid. They can only do exactly what you tell them to do, not what you want or need them to do." A series of children's stories, Amelia Bedelia, uses that theme too.

Her first gripe was that the computer didn't recognize the lower case "l" for the numeral "1" ad vice versa. Her old Smith-Corona typewriter didn't have different keys for those characters, or for upper-case "O" and Zero.