Further update re original documents: Passports arrived by mail on Sep 16th, all original documents arrived the very next day, Sep 17th. There were two pieces of mail, one addressed to me (containing my naturalization certificate) and one for my daughter (containing her original Canadian birth certificate and her green card).
I mentioned in an earlier post that the USPS clerk who took our application stated that the green card would not be returned to us. However, it was returned, which is consistent with experiences some other people have posted.
I infer that for LPR minors who acquire derivative US citizenship under the provisions of the Child Citizenship Act when their parent(s) naturalize, the card is left with the holder, as a piece of evidence needed to prove the person's US citizenship, until such time as they file N-600 to get a naturalization certificate of their own. (It's not compulsory to ever file N-600, though). If you do file N-600, then the green card will be confiscated at the oath ceremony, just as it is for N-400 filers. If you never file N-600, you need to make sure you carefully retain your primary evidence of citizenship, which is the combination of your birth certificate (showing parents names), parent naturalization certificate, and your green card. I presume (having no personal experience of this), that if your parents didn't stay together until naturalization you'd also need appropriate legal documentation of custody arrangements at the time of parent naturalization.
