Hi Jim
Der Mond is a great little opera, I have it on a recording (Munich Radio Symphony, Eichhorn) that includes Die Kluge. Sound quality not great but a pretty good performance. If you like Der Mond, you'd probably also enjoy Die Bernauren (also Eichhorn, better recording), a later work of Orff's. He was criticized for bowing to the Nazi regime with the 'fairytale operas' but I can't see the problem there.
One of my faves from that era was Hans Krasa - Brundibar, a Children's Opera. He was a Czech composer imprisoned at Theresienstadt. This was the Nazi 'model' concentration camp, the one where the artists and musicians went and the Nazis could point to to show what a rich life they give their prisoners. Delightful music, and it's completely obvious that Brundibar (the bad guy) represents Hitler. The last performance there was for a Red Cross inspection of the camp. After that the composer and performers (mostly children) were shipped off to their death at Auschwitz. Check on youtube, there's a ton of videos including clips of the original performance. I have a recording of this on a 3 cd set called 'Forbidden not Forgotten' a fine recording, but I notice there are a bunch of new recordings of this work that I'm not familiar with.