For anyone looking at going and/or taking kids:
If you live in Washington go to the DMV and order an 'Enhanced Driver's License'. They're about $10 more than a standard, but grant access to the borders by land or sea. (Some other states may offer them, so it never hurts to check).
If you have a minor (ages 16 and younger) you can get across the border with their CERTIFIED birth certificate.
If you're looking for transportation from Seattle:
From the airport you'll want to take the 'Link Light Rail'. Anyone at the terminals or getting baggage should be able to guide you, and their are a blue million stops. This will take you to Westlake Station. It's the very last stop on that ride, so it's nigh impossible to miss. This will put you in the heart of downtown Seattle for less than your favorite Starbuck's drink. From here you'll have 2 options:
If you want to Greyhound up to Vancouver, B.C. you'll have about a 6 block walk to their transit center. Once on the bus (I'd advise buying a ticket beforehand!) you'll be taken on up the beautiful town of Vancouver, B.C. You'll need to get a taxi (or learn the bus system there) because it's a bit of a walk from there to the convention center, but at least you're in the right city!
Alternatively, you can walk about 2 blocks from Westlake Station to the stop for the 510 express to Everette. This ends right outside an Amtrak train station with daily runs to Vancouver. Tickets run about $80 a person round-trip, but they're comfortable, fun, and drop off right beside another bus line that runs directly to the convention center. This is how me and the younger brother-in-law are making our way north.
Anyway, hopefully this helps someone out. I live just outside of Seattle, so if anyone needs help figuring out who what when where or why, just hit me up and I'll happily act as a guide, as best I can!