Huh? If they were 4 months old in October 2022, the infant would be 21 months old in March 2024.
While what you say is true it is entirely irrelevant here and no allegation of denied boarding was made, simply denied check-in due to a PNR without accompanying, valid e-tickets.
Straw poll this member base as to which airline might've been responsible for the lack of ticketing for a partner airline award, and I reckon you'd get about 90% response rate saying Qantas.
All this attack/questioning of the OP when it's just the latest in a very sad and long running saga of Qantas failing to deliver for customers. This is not an isolated incident. To coin a phrase, the airline is still not match fit...