Passport Considerations for Kids
The passport application process for adults is fairly straightforward. You file your application, with your photos and fees, at a passport office in your area. (For more information see the US Department of State passport page.)
For children the process differs in that the child and both parents or legal guardians need to be present when submitting their child's application. You can make special arrangements if one parent isn't able to submit the passport for the child in person, but expect some additional paperwork.
Additionally, if you have sole legal authority of your child or your child's other parent is deceased, you'll need to provide legal evidence of that.
Sue Antineau, who regularly travels to England with her two children, ages six and four, notes that even when you carry your child's passport you should still carry their birth certificates. Antineau's children are listed under their father's last name, while she kept her maiden name when she married. "It occurred to me that when I travel if I only have my kids' passports there's nothing to say that I'm their mother," says Antineau. "My name isn't anywhere on their passports."
A parent traveling without a spouse may also want to have a simple legal document that says the non-traveling parent agrees that the child may leave the country.