“A loud noise at one end and no sense of responsibility at the other.”
Definition of a baby, quoted by Colin Blakemore in his 1976 Reith Lectures, Mechanics of the Mind
The earliest print occurrence is credited to Elizabeth I. Adamson in the July 1937 issue of Reader's Digest, according to Quote Investigator https://quoteinvestigator.com/2017/01/10/baby/#note-15186-10.
Disputed