If you bring your son in with you on your first trip returning to the United States, he will be able to obtain lawful permanent residence as your derivative. Your girlfriend, however, will have a more complicated situation. You can file an immigrant visa petition for her, but she will not be an immediate relative. You will want to review if she will qualify for any other visas, and how long it will be for you to qualify for naturalization.
Answered on Dec 03rd, 2012 at 1:47 PM