Also I believe that qantas allows all guests under 12yo into their lounges hence why the whole family could go there.
Ah, now I'm starting to get it: although if the lounge receptionist had explained the reason I was being turned away, rather than trying to get rid of me, it would have been better.
I was unaware CX have different rules for status pax, and for oneworld. And the rules for Children are different in QF and CX, plus each have different rules for children, on oneworld if the lounge is not the carrier.
So, as I now get it:
CX F lounge:
Diamond Member: 2 guests, on CX or oneworld flight. Plus any child under 2.
oneworld Emerald: 1 guest, on CX or oneworld. Plus any child under 2.
QF lounge:
Platinum member on QF flight: one guest and up to two children (4-17) and infinite infants.
Platinum on CX: one guest and zero children plus infinite children under 3.
https://www.qantas.com/fflyer/dyn/fl...ts-of-platinum
So in theory QF will reject me for a child of 3 and over?
Not that it matters now, but I'd just arrived in Business on a Qantas flight - so maybe that rule would have trumped the Emerald rule, if I'd thought to whip out my arrival boarding cards?