In the Caribbean, as long as your passport is valid on the day you return to the US, you're fine.
That's how our status update worked too....I think final stages mean in the mail!
We got both the books and cards (for all of us) as we live close to Canada and would rather take the cards over the border than our books. Also, when we fly domestically, we use the cards as id for our kids (yes, I'm aware that kids do not need id but my oldest DS, when he was 12, was over 5'10 and weighed 165 and did not appear his age. I've had one too many arguments with TSA and having my DS go through the full body scanner and having to remove his shoes. According to TSA's rules, he does NOT have to remove shoes nor go through full body scanner--and yes, it matters to me).
It's most definitely "12 and under" not "under 12".
Argh, thanks for mentioning that. My eldest gets the "no way you're only 11!" every time but in a joking manner really... wouldn't be surprised if that's a girl vs boy thing. I'm making a mental note of the passport card idea for DS8 in a few years, or to investigate state IDs at least. It never fails to amaze me how surprised people are that the child of a really tall person would be, uh, really tall. One would think common sense might prevail when you see the family group.
The zoo in Seattle did it differently than the zoo in Tacoma, so I was constantly having to figure it out in the early years. 
We got the cards with our passports for the same reason, we are a couple hours from Canada! We had enhanced licenses before but now we can just use these.
