Green’s Dictionary of Slang

binnie one/two n.

[business n. (2) + number one n. (4)/number two n. (1)]

(Aus. juv.) urination/defecation.

[Aus]N. Keesing Lily on the Dustbin 48: One child ‘does its business’, talks of ‘binnie one’ or ‘binnie two’ or ‘number one’ and ‘number two’, and another ‘makes cackie’, or ‘poop’.