If they haven't seen a 3D printer or CNC mill work before, that might be a good demo for preschool, if you can make something really fast on it, that they can see evolve over a few minutes.
So they can see it, maybe ask teacher in advance whether they can stand around the table you've set up on, or what their seating arrangement is (on carpeted floor, movable low chairs, circle of chairs, array of desks, etc.).
Beware that 3D printers can aggravate respiratory problems, so maybe enclosed and ventilation hose to window. With CNC, you have to watch out for metal filings that can poke kids (and get transferred to eyes, etc.), or maybe short later electronics.
Bonus if you have time to show them one predetermined object, then go to make another object that has some choice for them in the design. Maybe you're making a cartoon character figure on a large 3D modeling thing (very quickly, speedrunning it) and you can ask them about the expression and things. Or maybe something for their teacher's, like a 3D "nameplate" for their desk, with some options for customization kids can choose, like font or decorations you put on it. (Unfortunately, probably can't do one of the kids' names, unless you brought enough print time for everyone, but having them make a personalized gift for their shared non-kid is good.) Try to think of things they can't do with poster paint, glue, and macaroni, without discouraging those media.
So they can see it, maybe ask teacher in advance whether they can stand around the table you've set up on, or what their seating arrangement is (on carpeted floor, movable low chairs, circle of chairs, array of desks, etc.).
Beware that 3D printers can aggravate respiratory problems, so maybe enclosed and ventilation hose to window. With CNC, you have to watch out for metal filings that can poke kids (and get transferred to eyes, etc.), or maybe short later electronics.
Bonus if you have time to show them one predetermined object, then go to make another object that has some choice for them in the design. Maybe you're making a cartoon character figure on a large 3D modeling thing (very quickly, speedrunning it) and you can ask them about the expression and things. Or maybe something for their teacher's, like a 3D "nameplate" for their desk, with some options for customization kids can choose, like font or decorations you put on it. (Unfortunately, probably can't do one of the kids' names, unless you brought enough print time for everyone, but having them make a personalized gift for their shared non-kid is good.) Try to think of things they can't do with poster paint, glue, and macaroni, without discouraging those media.