This one may come as a surprise to some judging by my taste in music, but this is 'Dona Nobis Pacem' - 'Grant Thou to Us Thy Peace'

Dona Nobis Pacem (Round - Rise Up Singing): https://youtu.be/69VG0YuZTHU

I chose this version over huge Choral arrangements because the four youngsters are about the same age as I was when I used to sing this very song. We also used to sing the Welsh version 'Dyro Inni Heddwch', which I cannot find performed. If anyone more adept on the YouTubes than me can dig it up I would love to hear it.

Dave.

Correction. As I cannot trust my memory I went to a respected University site for the composer. Turns out they are WRONG - it was Mozart. I'm sure the two men in question will not mind being confused - they were both great and can complain to me in person if there are any problems