Green’s Dictionary of Slang

1. a lavatory or privy [19C+ use is mainly (Aus./N.Z./US) ].

1743		Proceedings Old Bailey 23 Feb. 99/1: She wanted to go to the Little-house, but the Constable would not let her.
1772		Bridges Burlesque Homer (3rd edn) 534: Unless they work his bowels loose, / And make him run to th’ little house.
1797		Bridges Burlesque Homer (4th edn) II 409: Unless they make his bowels loose, / And make him run to th’ little house.
1804		in N.E. Eliason Tarheel Talk (1956) 282: New cellin [i.e. ceiling] to the Little House.
1824		History of Gaming Houses & Gamesters 41: Two others [i.e. gambling clergymen], very irreverently packed up in a little house across the yard, not usually talked of at dinner time.
1888		S.O. Addy Sheffield Gloss. 136: Little house, a privy.
1941		Baker Popular Dict. Aus. Sl.
1988		McGill Dict. of Kiwi Sl. 70/1: little house, the toilet.
2003		McGill Reed Dict. of N.Z. Sl. [as cit. 1988].

2. (US Und.) a local prison; a reformatory.

1931		Irwin Amer. Tramp and Und. Sl. 122: Little House – A reformatory.
1949		Monteleone Criminal Sl. (rev. edn) 146: little house A reformatory.
1956		N. Algren Walk on the Wild Side 16: They [...] boasted of their time in jail. Hard time and easy, wall time and farm time, fed time and state, city time, county time, short time and good time, soft time and jawbone time, big house, little house and middle house time, industrial time and meritorious time — ‘that’s for working your ass off’.