Sure, all babies need passports to fly over the U.S. border and back, but if you think you can slip through airport check-in and onto the plane for a domestic flight without presenting any ID for your child under 2 years old, you might be making a costly mistake in time as well as in money. Updated for 2018.

One of the most frequent misconceptions I hear from parents preparing to fly with their babies and toddlers is that they don’t need ID for their child on domestic flights. 

It’s also one issue I hope to clear up right here, right now, so that even those of you who have already flown without presenting ID for your babies (as I have done myself on many occasions) won’t find yourselves in a sticky situation down the road.

First, let’s just be clear. It’s not about security.

There’s only one reason that baby is riding free on your lap within the U.S.—or in his own seat for a reduced “infant fare” that is not extended to children over 2 years: his age.

It stands to reason that at some point, the lap child you may not have been asked to present a birth certificate for at 6 months of age might spark new interest when you arrive to check in for a flight at 22 months. Or perhaps even at 15 months, depending on the person checking you in for your flight and his or her experience—or lack of experience—with babies and young children.

In all fairness, many parents do try to squeeze in one last free flight just before a child’s second birthday—and even just after thinking they’ll still get away with it. A few bold parents have tried to push it even farther, and I’ve heard some hilarious stories about attempts to check in petite passengers who, when asked at the counter, were able to quite articulately explain to the ticket agent how old they are and also how old their mommies told them to say they were.

From a couple of popular U.S. airlines:

• Southwest Airlines: “A birth certificate is required to validate the age of all infants under age two.” (Tip: If you set up age-verification with Southwest, you can save this step and use online check in next time around–see details in my post on flying Southwest Airlines with a baby or toddler here.)
• JetBlue : “Customers traveling with a lap child will be asked for proof of age, such as a passport, birth certificate (copies are acceptable for domestic travel) or an immunization record. Infants between three and 14 days old must also have, in the form of a letter, their doctor’s approval to travel.”

The bottom line is this: Airline personnel are entitled to ask for proof of your child’s age any time your child is flying for free or for a reduced fare based on age. And sometimes they do – sometimes when the parent may least expect it.

So hopefully you won’t ever be caught off guard by this yourself, and risk missing a flight or having to purchase an on-the-spot ticket for your child.

What happens after 2 years?

Generally, children 2 years and older pay the same fare as adults for flights within the U.S., so this is not an issue once your child is riding in a seat that costs the same as your own. You might have other reasons, however, why you would want to have your child’s ID along on these trips.

For more planning tips and advice on planning domestic and international flights with young children, see Part 5 of Travels with Baby. And why take any chances? Keep on-the-go tips for your airport waits and flight at your fingertips with the Take-Along Travels with Baby (in pocket-size or ebook edition).