You will see conflicting information in the different posts above...
To avoid confusion... To go to Canada and back you are crossing the border twice.
Entering Canada you play by Canada customs rules
Returning to the US you play by US customs rules
They aren't the same rules. Using one of the links above you can find this info
ENTRY / EXIT REQUIREMENTS:
Entry into Canada is solely determined by Canadian Border Services Agency (CBSA) officials in accordance with Canadian law. Please see the CBSA’s website
for details. Canadian law requires that all persons entering Canada carry both proof of citizenship and
proof of identity. A valid U.S. passport, passport card or NEXUS card (see below) satisfies these requirements for U.S. citizens. If U.S. citizen travelers to Canada do not have a passport, passport card or approved alternate document such as a NEXUS card, they must show a government-issued photo ID (e.g. Driver’s License) and proof of U.S. citizenship such as a U.S. birth certificate, naturalization certificate, or expired U.S. passport. Children under 16 need only present proof of U.S. citizenship. (Please see below for important information concerning re-entry into the United States).
If you plan to travel to Canada with a minor who is not your own child or for whom you do not have full legal custody, CBSA may require you to present a notarized affidavit of consent from the minor’s parents. Please refer to the CBSA website linked above for more details. There is no specific form for this document, but it should include dates of travel, parents’ names and photo copies of their state-issued IDs.
When returning to the United States from Canada, it is very important to note that all
U.S. citizens are required to present a valid U.S. passport to enter or re-enter the United States via air
. For entry into the United States via land and sea borders
, U.S. citizens must present either a U.S. passport, passport card, NEXUS card, Enhanced Drivers License or other Western Hemisphere Travel Initiative (WHTI)-compliant document. The only exception to this requirement is for U.S. citizens under the age of 16 (or under 19, if traveling with a school, religious, or other youth group) who need only present a birth certificate (original, photocopy or certified copy), Consular Report of Birth Abroad, or naturalization certificate.
American travelers are urged to obtain WHTI-compliant documents before entering Canada well in advance of their planned travel. For the most recent information on WHTI and WHTI-compliant documents, please see the State Department’s website
(http://travel.state.gov/travel/cbpmc/cbpmc_2223.html - broken link).