And the children of citizen of the United States that may be born beyond Sea, or out of the limits of the United States, shall be considered as natural born Citizens: Provided, that the right of citizenship shall not descend to persons whose fathers have never been resident in the United States
Citizens is plural. The Constitution stated that only a natural born citizen could be President, in order to prevent any possibility of divided loyalty.
So is children. "Children of citizens" is referring to the entire body of cases. That interpretation is better because the line you quoted goes on to say that only the father has to have been resident in the USA.
That is one parent.
It said: "...all children, born out of the king's ligeance, whose fathers were natural-born subjects, are now natural-born subjects themselves, to all intents and purposes, without any exception; unless their said fathers were attainted, or banished beyond sea, for high treason; or were then in the service of a prince at enmity with Great Britain."
“Citizens is plural. ..”
fatherS is also plural. Does that mean the children need to have two fathers?
“fathers have never been resident in the United States”
It looks like when it says citizenS, they mean citizens of many children which is why they made it plural.