C.S.
Dear F. B.,
When I got my last car, we were a family of three. Believe it or not, I got a Sienna mini-van - 7 seater. We got it because we like to road trip and wanted to be comfortable with a baby and related gear and wanted to be able to take it camping:) A few years later we had baby #2, and now they are older and like to take friends with us or carpool. I often have 4-5 kids with me and wish I had the 8 seater:) I can't imagine having a smaller vehicle until they go to college!
I used to live in DC so I understand being a one car family and wouldn't suggest a mini-van since it is easier to get into smaller spaces. Just keep in mind that only children really like to bring friends with them! So you probably want at least a 5 seater! Also, even though as they get older you don't need strollers and car seats you do need sports equipment!!!
Good luck!