enfant de coeur

noun1

1. •
   (no longer used) A child who sings in a choir, typically quiet and well-behaved.

   • "Nowadays, the young people sit while their elders stand!" the Abbot succinctly said, riveting a curly-pated enfant de coeur lolling coxcombically beneath the nose of a doating Statilia. — 1919