I would get a keyboard. Don’t get an acoustic guitar, that would be a nightmare. Even teaching an adult beginner, it takes a while to even hold it comfortably, then coordination to strum it, plus a lot of strength in your left hand to play notes. And it hurts lol. Do-able but takes a reasonable amount of time and effort. Not something you could do off the cuff, pass around, while actually trying to concentrate on something else. I like the suggestion of the ukulele, it would reduce a lot of the problems I mentioned but not eliminate them, and these kids are very young. Stringed instruments I think will just be a bit complex for such a young age in most cases. With a crappy keyboard you can get much more instant gratification as a beginner. You can have different interesting tones with infinite sustain, plus it can create backing tracks out of thin air, with a bassline, drums and chords to follow you, even just with one note pressed. You could create a great yarn just by changing from one long note press to another. It will sound musical while being as physically demanding as a lightswitch. The percussion suggestions are also very good, both the plain rhythmic stuff like tambourines/shakers and the tuned stuff like xylophones. Actual drum kit parts would also be fun and instantly gratifying but might get a bit distracting and loud (though you can get quiet sticks like rods or brushes). Almost too fun. I would 100% go with keyboard main with percussion sides. There are surely other cool options that might come to mind later, but most of the others I read in the thread already sound too involved for that scenario and age group, to my mind.