A little boy who gets into a house through the sink-hole, and then opens the door for his accomplices: he is so called, from writhing and twisting like a snake, in order to work himself through the narrow passage.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Little Ease * Live LumberNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes