The most useful and interesting letters we get here from home are from children seven or eight years old. [...] They tell all they know and stop.
Sometimes misquoted as: The most interesting information comes from children, for they tell all they know and then stop.
Mark Twain Speaks for Himself (Purdue University Press, 1997), p. 58, "Mark Twain's Idea of a Good Letter", December 6, 1869