enfant de coeur

Etymology
Borrowed from.

Noun

 * 1)  A child who sings in a choir, typically quiet and well-behaved.
 * 2) * 1919, Ronald Firbank, Valmouth, Duckworth, hardback edition, page #88:
 * "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.