Bring the birth certificate for a lap baby. You have to prove age for an age-based fare, even if that "fare" is free.
We've flown Jet Blue, United, American, and either US Airways or Continental with a lap baby and have never been asked for any proof of ID or age. Even when he was 18 months old. I can't remember which, but a few if the airlines printed him his own boarding pass, so they asked to see him when we checked in, but that's all. We still brought a copy of his birth certificate, just in case.
Customers traveling with a lap child could be asked for proof of age, such as a passport, birth certificate (copies are acceptable for domestic travel) or an immunization record when the infant's age is questionable. Infants between three and 14 days old must also have, in the form of a letter, their doctor's approval to travel.
Infants must be traveling with an adult customer at least 14 years or older, and the infant must sit on the adult's lap during takeoff and landing.
We are flying Southwest in less than a month. I called in to add my 17 month old to the reservation and she said that I would need to bring a copy of the birth certificate which has already been placed with our travel documents
We flew Spirit last December and took the certificate with us but they never asked for it.
My theory is to take it and be more prepared than unprepared at the airport.
I would hope that proper i.d. would always be required for very young children, for safety and security issues for the child. After all how does anyone really know that you are the proper legal guardian or other designated adult? I know there are stories in the past of flight attendants not being so sure of this sort of thing, long ago before regulations and policies were either changed, or created.
If I was ever to see anything questionable, I don't care what it is on an airline, even if it is but a puddle jumper, I will open my mouth at the appropriate time.
Wow, guess we lucked out. When our son was a lap child we flew about 10 times with him and no one had ever asked for his birth cert. thank goodness as I never brought one! He did get his passport at 2.5 and had his own seat/fare. Our daughter flew 3 times as a lap child and again never was asked for her birth cert. and it was last year when we flew with her as a lap child.