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/
没有经过这种“documented”的孩子,不能证明是美国公民,因为他们无法申请美国护照和其它福利。不是美国公民也不涉足美国本土做生意当然也就不存在给美国交税的义务。