LATER:
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 other travel document approved by the Department of Homeland Security.
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 U.S. citizenship such as a naturalization certificate or citizenship card.