Using an app, like Tonepad, take turns in adding or editing 3 notes per turn and compose a fun little ditty. Or without the app, try it on a piano. Have one person play a few notes, timed within 8 beats, over and over, and a second person adds their notes, and maybe a third person too if you squeeze together. After all three are playing their music within the same 8 beats, the first person can change their notes. A metronome may be handy - which could be a free app also.
