The Passport was not needed when we crossed from Belgium to France. The highway narrowed and people slowed slightly as we drove through what used to be a crossing checkpoint.
Updated 2012/05/29: Renewed passports for kids and wife today. We went downtown to Seattle to the Passport Authority on 5th and Yesler. I didn't realize you can go into any Post Office to renew or get passports for kids. Could have saved on the automatic expediting fee they tag on when you go to the Passport Authority.