Green’s Dictionary of Slang

(N.Z.) a nappy or diaper.

c.1940		R. Mason postcard (1953) in DNZE 522/2: Heard nap for napkin in Dunedin .
1959		G. Slatter Gun in My Hand 104: Keeping kids off the flowers. Wiping up the pee on the floor. The stink of naps in the laundry.
1989		Eve. Post (Wellington) 18 Oct. 33: We ‘special people’ had a good night out. We found that old-fashioned naps are better than throwaways – and a two-pinner is still more watertight than a one-pinner.