If your spouse was a U.S. citizen when your green card was approved, and if you're still living together 3 years after your green card was initially approved, you can apply for U.S. citizenship after 3 years -- and when you are approved, your unmarried children under the age of 18 can become U.S. citizens automatically (by "action of law") so long as they are (a) lawful permanent residents; and (b) still living in the U.S. citizen parent's custody.
Unfortunately, children who were over the age of 18 years -
Unfortunately, children who were over the age of 18 years when they initially got their green cards (were granted lawful permanent residence) have to wait 5 years before applying for U.S. citizenship despite the fact that their parent only had to wait for 3 years.
Children who were under the age of 18 years when they got their green cards -
Children who were under the age of 18 years when they got their green cards (granted lawful permanent residence) but over the age of 18 years when their birth parent got their U.S. citizenship do not automatically become citizens and also have to wait 5 years before applying for U.S. citizenship - despite the fact that their parent only had to wait for 3 years.
How do I establish that my child has U.S. citizenship automatically?It is important to do BOTH:
1. Apply on behalf of the child for a U.S. Passport so that he or she has evidence of U.S. citizenship.
2. Submit an "Application for Certificate of Citizenship" (Form N600) to the USCIS to obtain a Certificate of Citizenship.
There are many legal battles over whether a U.S. Passport is sufficient proof of U.S. Citizenship or not.
A good parent will make sure their child has both a U.S. Passport and a Certificate of Citizenship. By the way, a child who receives U.S. citizenship automatically may obtain their passport or Certificate of Citizenship at any time (even if they are over 18 years of age).