Children born outside the U.S. who have at least one parent who is a U.S. citizen acquire citizenship at birth. In order to prove citizenship, the child must have a Consular Report of Birth Abroad. This can be obtained by the child, the child’s parent or parents, the child’s guardian or someone acting in loco parentis. The document does not take the place of a travel document and functions only as proof of citizenship that can be used to obtain a passport or visa or in any other situation requiring proof of citizenship.
www.uspassporthelpguide.com/ds-2029-application-for-consular-report-of-birth-abroad-for-a-u-s-citizen/
沒有經過這種“documented”的孩子,不能證明是美國公民,因為他們無法申請美國護照和其它福利。不是美國公民也不涉足美國本土做生意當然也就不存在給美國交稅的義務。