In Grade 5, my teacher took us to the theater several times; on one occasion, we saw a children’s chorus perform two musical plays. One of these I have managed to identify as “The Golden Vanity” by Colin Graham and Benjamin Britten. The other I have not so far and will describe what I remember of it here. It was a pretty typical Commedia dell’arte-type story, in which Harlequin and Columbine wanted to get married; Columbine was the daughter of a rich merchant (like Pantaloon in Commedia dell’arte, though as I recall, he was referred to as “the Operatic Father”), who wouldn’t allow it, but Columbine’s duenna acted as an intermediary between her and Harlequin and it somehow worked out in the end. There was another layer to the performance, though. An adult narrator explained the choral accompaniment to this opera by telling a story of a troupe of musicians who couldn’t pay their bill at an inn, so the inkeeper confiscated their instruments. They went to a wise man for help and he advised them to use their voices in their performances - so the choir in the background imitated musical instruments.
Could this have been another piece by Graham and Britten?