All persons traveling by air outside of the United States are required to present a passport or other valid travel document to enter or re-enter the United States.
On June 1, 2009, the U.S. government will implement the full requirements of the land and sea phase of WHTI. The proposed rules require most U.S. citizens entering the United States at sea or land ports of entry to have a passport, passport card, or WHTI-compliant document.
CHILDREN: U.S. citizen children under the age of 16 will be able to present the original or copy of their birth certificate, or other proof of citizenship such as a naturalization certificate or citizenship card. More information on US Passport requirements can be found at http://travel.state.gov/content/visas/english/visit.html