Quick question that BA and AA seem to be confusing about. I'm about to get some shorthaul awards through BA on a domestic US flight. Infants in arms would be totally free if this was a ticket bought from AA. When I put an infant in the BA calculator it charges 10%. It's only 450 avios, but do I need to tell BA about the infant? Or should I just get the adult tickets and ask AA to add the infant-in-arms?

Thanks.