As of june 1, 2009 ALL Canadians need a passport to enter the USA
http://www.ppt.gc.ca/planification/usa.aspx?lang=eng®ion=Canada
I just received ours for the kids, it took less than 4 weeks by sending them in by mail.
Holly
The link provided states:
"The Western Hemisphere Travel Initiative (WHTI) is a US law that requires all travellers, including US and Canadian citizens, to present a valid passport
OR OTHER APPROVED SECURE DOCUMENT when entering the United States.
For information on travel documents required for travel to, from or through the United States, please consult the website of the Canada Border Services Agency,
http://www.cbsa-asfc.gc.ca/whti-ivho/child-enfant-eng.html
There you will find the following information:
All Canadian citizens (including children) travelling into the USA by
AIR must present either a passport or a NEXUS card.
When entering the USA by land or sea (and since the OP stated they are driving, this applies to them)
"Canadian citizens aged 15 years or under are only required to present proof of Canadian citizenship, such as an original or a photocopy of a birth certificate, or an original citizenship card, when entering the United States by land or water. Canadian citizens 18 years of age or under who are travelling with a school or other organized group, under adult supervision with parental/guardian consent, may also present proof of Canadian citizenship alone".