Originally Posted by
nutwpinut
Do you need a letter even if the kid has a passport? I'm planning to bring my son, who will be 6, to London next year.
"Hague Convention on Abduction" to put it succinctly . USA became a signatory 1 July 1988.
You need a notarized letter of authorization from the missing parent or other documentation demonstrating sole custody.
See USCBP information
here.
If a child (under the age of 18) is traveling with only one parent or someone who is not a parent or legal guardian, what paperwork should the adult have to indicate permission or legal authority to have that child in their care?
U.S. Customs and Border Protection (CBP) strongly recommends that unless the child is accompanied by both parents, the adult have a note from the child's other parent (or, in the case of a child traveling with grandparents, uncles or aunts, sisters or brothers, friends, or in groups*, a note signed by both parents) stating "I acknowledge that my wife/husband/etc. is traveling out of the country with my son/daughter/group. He/She/They has/have my permission." See our Q&A parental consent.
Under the Convention, other countries may impose the same requirements. You may not be asked for this documentation, but on the other hand you risk not being admitted and immediate return.
Sample printable letter and information
here.
Additionally, a letter authorizing securing medical services may be useful for a child traveling with grandparents, a group, friends, etc.