Buying ticket for infant not yet born

Hi - I just tried to buy a ticket for my son who will be born in August, but secure flight requires a birthdate in the past in order to allow ticket to be purchased (even for lap child). I just entered yesterday's date in order to get the computer to take the reservation.

Does anyone know if this will cause trouble at the airport? I don't think an infant even requires ID to fly. Do I need to call tomorrow within the 24 hour cancellation period to adjust this?

Thanks in advance,
New parent to be!