The story
From kid + nap (“to nab; to grab”). Originally Thieves' cant, referring to the practice of stealing children and shipping them to colonies or plantations as laborers. First attested c. 1680.
First known use, by meaning
- from 17th c. To seize or detain (a person) unlawfully and transport or conceal them, sometimes for ransom.
Etymology from Wiktionary, CC BY-SA 4.0.