§ 320 (8 USC 1431) Children born outside the United States and residing permanently in the United States; conditions under which citizenship automatically acquired
A child born outside of the United States automatically becomes a citizen of the United States when all of the following conditions have been fulfilled:
At least one parent of the child is a citizen of the United States, whether by birth or naturalization.
The child is under the age of eighteen years.
The child is residing in the United States in the legal and physical custody of the citizen parent pursuant to a lawful admission for permanent residence.
Subsection (a) of this section shall apply to a child adopted by a United States citizen parent if the child satisfies the requirements applicable to adopted children under section 101(b)(1) of this Act [8 U.S.C 1101(b)(1)] .