I'm facing a similar issue with AA and EY for a redemption on EY.
Called EY who said they can't touch the reservation as it's made by AA and that AA should be able to sell me the infant fare.

Will I be able to get AA to quote me a return infant fare on EY for an adult travelling on 2-one way tickets? I recall seeing something on FT a while back but can't find it any more.

Thanks!