I managed to get return infant tickets booked in the past, although it was very complicated and took forever to achieve it. It also caused a LOT of confusion at check-in at various points, because we had actually booked stop-over trips for adults on separate tickets (Think AAA-BBB // BBB-CCC, then CCC-BBB // BBB-AAA), and then managed to book BBB-CCC-BBB for the infant. We managed t get on all flights, but boy did it take some time to explain to the check-in agents...

Still better than that one time when we were flying QR SIN-DOH-FRA on miles in C, with separate an infant-in-lap ticket that I had bought two months prior, at the airport in SIN, with a QR agent speaking over the phone to QR HQ in DOH, only when it came to check-in at Changi two months later, the agent there informed us after 45mins of trying to figure out what was going on, that the infant ticket had been issued in economy class... (How is that even possible?!). It took them almost two hours to sort it all out, and they held the plane for us, while SIN's QR staff tried to call DOH again to remedy the error they had made, and in the end the check-in staff informing the flight crew to hold the flight because "the pax had been held up at immigration (!)"... which obviously was total BS, the ground staff simply did not want to admit to the flight crew that they had f***ed up our ticket...

All in all, I can only say that I am very glad that my younger daughter turned two earlier this year. Finally I don't have to deal with all the ball-aches of trying to link infant tickets to adult award tickets, especially across different airlines in the same alliance!