I see your comment a lot and I finally think it should be commented on.
Citizens (plural) could describe all the citizens(pleural) of the US, not all the parents(pleural) of the children.
For example there are "Children of Veterens Tuition Grants". Verterens (plural) doesn't describe a requirement for a child to have two veteren parents. It instead is plural to describe all the veterans who have children.
Well......I'm certainly glad you did ! Nothing like a comment on a comment.........
It also (just possibly) might mean....."Born of two citizen parents" as described in Vattel's mid 18th century classic......and still quoted by the U.S. Supreme Court more than half a century later!