Travel By Land or Sea
If you're traveling by land or cruising, your driver's license and children's birth certificates are still valid for minors when your destination is Canada or Mexico (however, all adults should carry a passport), according to the US government. So for example, if you take a cruise that originates in Florida and travels to Mexico, your child can still travel without a passport onboard the cruise ship. Yet it's a safer bet for all family members to travel with passports.
"No matter how you are traveling outside the US," says Kelly Klundt, a spokesperson for the US Customs and Border Protection office, "be sure to check that country's guidelines on passports." She cites that some countries, such as Mexico, will occasionally allow US citizens to enter and exit the country without a passport, other countries may not.
Klundt adds, "Cruise vessels may have stricter requirements" meaning that the cruise line may demand you use a passport even if the US government doesn't. "As far as the government is concerned if you're traveling by land or by sea you don't yet need a passport to come back into the country, but we highly encourage travelers to bring proof of citizenship with them," says Klundt.
US citizens should expect passport rules to go into effect for land crossings in January 2008. The US Passport Agency expects another jump in applications with the additional regulation.