Definition - a child whose inopportune remarks cause embarrassment
The first thing you should know about enfant terrible is how to pluralize it, since these beasties often travel in packs: it is enfants terribles. The word has other, non-childish meanings, including “a person known for shocking remarks or outrageous behavior,” and “a usually young and successful person who is strikingly unorthodox, innovative, or avant-garde.” These came about in the early 20th century; the oldest sense (your brother/sister’s spawn) dates back to the middle of the 19th century. Enfant terrible was taken directly from the French, in which language the literal meaning is “terrifying child.”
”Well, she wath in her pinnafaw, wathn’t she, ma?” says Hugh, quite unabashed; which question Lady Hawbuck turned away with a sudden query regarding the dear, darling daughters, and the enfant terrible was removed by his father.
— The Era (London, Eng.), 18 Oct. 1846