Immediate relatives
Immigration law allows U.S. citizens to petition for immediate relatives to come and live permanently in the United States. Immediate relatives of a U.S. citizen are the U.S citizen’s spouse, unmarried children under the age of 21, orphan adopted by a U.S. Citizen and the parents of a U.S. citizen who is over the age of 21. Immediate relatives have special immigration priority and always have a visa number immediately available because there are an unlimited number of visas for their particular categories. You can apply for a green card whether you are inside or outside of the U.S.