Green’s Dictionary of Slang

(N.Z.) an illegitimate child.

1985		J. Sherwood Botanist at Bay 120: The fat slob of a middle-aged secretary carrying a torch for her employer and even looking after his illegit.
2008		D.R. Pollock ‘Pills’ in Knockemstiff 53: She always came back with [...] something sweet for her two illegits.