Because of this rule, unusual cases have arisen whereby children have been fathered by American men overseas from non-American women, brought back to the United States as babies without the mother, raised by the American father in the United States, and later held to be deportable as non-citizens in their 20s. The final element has taken an especially significant importance in these circumstances, as once the child has reached 18, the father is forever unable to establish paternity to deem his child a citizen.