[tharkun__]

Not entirely correct. With a Beibehaltungsgenehmigung you can also obtain other citizenships than what you mentioned and it doesn't need to be by birth. They do make you answer all sorts of questions though to give you that certificate.

Source: we went through it.

We also had a similar-ish experience passport wise while the kids had non-German passports only while we only had a German one. We held up the line of cars waiting to get on the ferry to England (going from the Netherlands) for quite some time while they asked and checked why some Germans were driving Canadian kids to England: o see the Scottish Highlands, duh :)

[fakedang]

What GP meant was that USA treated the child as a US citizen by descent, in spite of the lack of a passport, which is why immigration mandated that the child should have been issued a US passport before traveling to the US. It's natural for a lot of countries that allow dual citizenship to mandate that you travel to said country with the passport of that place.

[tharkun__]

I completely understand and the two paragraphs in my comment are two separate things. One comments on the fact that they said you can only have another citizenship by birth if you want to keep the German one (false) and the other one reminded me of another sort of funny passport and different/dual citizenship situation from my life, which is why I said "similar-ish". Emphasis on "ish".