Be mindful that the rules have recently changed in that now in order to be eligible for an infant ticket, the child has to be less than 24 months old for the entire journey. It used to be that they had to be less than 24 months old for the first leg only.

BTW, I just travelled with my 15 month old kid as a lap child, and I've now decided that unless the flight is empty and I can be reasonably sure that I can get an extra empty seat next to us anyway, I'm going to suck it up and buy a child ticket unless the flight is very short.

Also slightly OT, but one definite heart-breaking aspect of travelling with young kids is that one invariably gets offered an op-up that needs to be declined