Green’s Dictionary of Slang

sugar baby n.

also sugar daddy, sugar mummy

(N.Z. prison) a visitor who brings in a supply of contraband.

[NZ]D. Looser Boobslang [U. Canterbury D.Phil. thesis] 181/1: sugar baby (also sugar daddy or sugar mummy) n. a visitor, partner or pimp of an inmate, who brings the inmate a supply of drugs, money, or other goods.