Traveling overseas with your baby? Be sure they have a valid passport, passports are required regardless of age. You can learn all about applying for your child's passport here.
If you are traveling internationally with a child without one or both parents you will need to provide proof of consent from the other parent or parents. You can make a free travel consent form here. If you have sold custody of the child you will need to provide proof which can be:
Documents Needed for Domestic Travel
Children under the age of 18 traveling on domestic flights do not need to show identification. However, if they are traveling as a non-ticketed lap child the airline has the right to ask for proof of age. The most accepted forms are a birth certificate or passport. Some airlines also allow immunization records as a form of ID but I would double check with the specific airline.
I have yet to be asked for ID for my children but I carry their passports with me each time because, better safe than sorry. Once at the airport I saw a very angry parent get turned away when the he couldn't provide proof of age for his lap child. The gate agents would only allow him to board the flight with his daughter if he paid for a ticket for her on the spot since he could not prove she was under 2. Of course buying a plane ticket right before the flight takes off will be very expensive and there is no guarantee the flight would even has open seat available to purchase.