SEC. 3. And be it further enacted, that the children of persons duly naturalized, dwelling within
the United States, and being under the age of twenty-one years at the time of such
naturalization, and the children of citizens of the United States born out of the limits and
jurisdiction of the United States, shall be considered as citizens of the United States. Provided,
that the right of citizenship shall not descend on persons whose fathers have never been resident
of the United States. No person heretofore proscribed by any state, or who has been
legally convicted of having joined the army of Great Britain during the late war, shall be admitted
as foresaid, without the consent of the legislature of the state in which such person was proscribed.
The provision for children of citizens born “out of the limits of the U.S.” is why McCain is a citizen, and not a natural born citizen. Congress can and did extend limits to include embassies and specific military installations, but The Canal Zone was not one of them until 1937.
If my understanding is correct, a specific declaration is not required. If Vattel is the basis of the founder's understanding of the term "natural born citizen" (and it is our argument that it IS based on Vattel) then we must accept Vattel's position on the status of children born to citizens serving their country.
Not only that, but it just makes sense to regard the children of Soldiers as natural Americans. It is the father that imparts allegiance according to the ancient rule, and what better example can be set of love of country than risking or losing your life in it's service?