請參看USCIS的說明的這一段:
Relatives
A Permanent Resident can petition for some relatives to join him or her in the United States as immigrants. Those relatives are your spouse and children, regardless of age. See our page on "Immigration through a Family Member". 鏈接如下:
http://www.uscis.gov/portal/site/uscis/menuitem.5af9bb95919f35e66f614176543f6d1a/?vgnextoid=fe17e6b0eb13d010VgnVCM10000048f3d6a1RCRD&vgnextchannel=4f719c7755cb9010VgnVCM10000045f3d6a1RCRD