Just a data point for whoever planning to travel with lap infant on AS award ticket. SQ will NOT sell you an lap infant ticket for your SQ flights booked by AS miles. I got some hope at first when SQ (and also AS) added my kid to my reservation and SQ even gave me a price quote for that ticket (unfortuantely, it was through email). However when I called SQ office to pay for it (as instructed by SQ email), no one had a clue of what I was talking about. SQ agents keep telling me the same thing "It's an AS's ticket, AS has to issue the lap infant ticket" . So after almost 4 hrs+ on the phone with them, I just give up. Luckily, there is a price drop and it makes more sense to pay cash for the flight and save my 100k AS miles.

On the other hand, JAL has no problem selling you lap infant ticket.