Well, Eve, I didn't mean any heavy music theory for beginners, just what the notes are and there's no note between E and F, B and C, level theory.
So here's a dumb question but you got me here, give me an example of a one chord song? I can't think of one. Neither of my students expressed an interest in singing when I asked so I hadn't thought much aboout it but I'd use it if I thought it would motivate them.
Can you get them to even hold the strings down in the first lesson? I always got, "That hurts!" to which I'd answer that in music there's a saying that "You got to pay your dues" and this is the first payment but it will get better in a week or two.