Make life easy. Get a passport.
Now, officially, you don't need a passport until 2007, according to our local travel agency, if you're going to Canada or Mexico. But you do need photo ID and your original birth certificate.
It's not so much leaving the country as it is getting back in.
When we went to visit my folks in Canada at Christmas, we brought our photo ID's and copies of the kids' birth certificates. At that time, that was sufficient. I also have a Resident Alien card, since I'm still Canadian.
This time around though, soon after the foiled terrorist plots with the planes from Britain, the US is being even more diligent (rightly so) about checking identification. I didn't realize we needed the original birth certificates, not just for the kids, but for all of us. We wound up spending a night in Bellingham, WA so I could coordinate with our neighbors to get into our house, sort through my mess of a filing cabinet (at least all of us have an individual file), and then they FedExed our stuff to my folks. We didn't want to cross the border without knowing they had all the documents in hand first.
Once that was established, we were fine to go into Canada. 3 days later, we had our documents so we could head home a few days after that.
Just so you know this wasn't overkill, once we made it to the US border (after a 50-minute wait in a long line of cars), the officer asked to see each of the kids and checked all our ID's against our photos. He verified the names on the birth certificates, and he even ran my information on the computer as he did all that. Again, we will wait however long they need us to in order to keep the nation safe. I live here, and I appreciate the diligence.
I am in the process of getting my Canadian documents so I can renew my passport. I'll be getting the paperwork together for Lee & the kids this week as well.
It's a shame the media has been so disappointed - first, nothing got blown up for them (aw!) and then, no one is even getting mad about the "hassles" of travelling. I feel so sorry for them - NOT!