Green’s Dictionary of Slang

(Aus.) conventional, respectable, and thus, by criminal standards, naïve; small-scale.

1991		M.B. ‘Chopper’ Read Chopper From The Inside 95: The reason most guilty men walk free is because poor old mum and dad juries simply find the evidence impossible to believe.
2021		C. Hammer Opal Country 212: Not the big players, not the hedge funds and whatnot, but retail. Mum and dad investors.