1. The Green Card Application for U.S. Citizen's Unmarried Children under 21 Year of Age

Unmarried children under 21 year of age of U.S. citizens are eligible to apply for permanent resident status as immediate relatives. Immediate relatives of a U.S. citizen can immigrate to the United States without being subject to any numerical restrictions. This means there is no visa quota allowed under the immediate relative category, unlike other close family members of U.S. citizens or permanent residents. 

The immediate relatives of U.S. citizens do not have to wait for an immigrant visa number to become available once the application filed for them is approved by the U.S. Citizenship and Immigration Services (USCIS). 

2. U.S. Citizen's Unmarried Children over 21 Year of Age, in the First Preference Category

A child of a U.S. citizen, who is seeking U.S. permanent residency and who will turn 21, will be age out and lose the original eligibility as an immediate relative of U.S. citizen. In most cases, if the child turns 21 before the adjustment case is approved, the case moves into First Preference category which can result in a delay in the processing time. 

If a child does not qualify as an immediate relative, he or she may apply under the First Preference - unmarried children over 21 year of age of U.S. citizens (23,400 per year, plus unused visas from the Fourth Preference). Since numerical caps apply to this category, visa petitions are ranked chronologically based on a "first come, first serve basis." Also, because of the numerical cap, there may be long waiting period to obtain a visa. 

3. U.S. Citizen's Married Sons or Daughters, in the Third Preference Category

This category is designed for the married children of U.S. citizens regardless of his or her age. That means to qualify as a "child" in this category, the person must be the son or daughter of a U.S. citizen, who is married. A “married son or daughter” is a person who has a recognized parent-child relationship, and who is also married, regardless of age.

Married sons and daughters of U.S. citizens, including their spouses and their minor children, have an immigrant visa number of 23,400 per year, plus unused visas from the First and Second Preferences. Immediate family members of the married alien child can also apply for a Green Card with the child. 

4. Required Documents for Child/Parent Relationship

As a parent, the document to prove your child/parent relationship include: 

1) A child and you are the mother: Submit a copy of the child's birth certificate showing your name and the name of your child. 

2) A child and you are the father: Submit a copy of the child's birth certificate showing both parents' names and your marriage certificate. 

3) A child born out of wedlock and you are the father: If the child was not legitimated before reaching 18 years old, you must provide copies of evidence that a real parent-child relationship existed between the father and the child before the child reached 21 years. This may include evidence that the father lived with the child, supported him or her, or otherwise showed continuing parental interest in the child's welfare. 

4) Stepparent/stepchild: If your petition is based on a stepparent-stepchild relationship, you must provide a copy of the marriage certificate of the stepparent to the child's natural parent showing that the marriage occurred before the child's 18th birthday, and copies of documents showing that any prior marriages were legally terminated.   

5) Adoptive parent or adopted child: If you and the person you are filing for are related by adoption, you must submit a copy of the adoption decree(s) showing that the adoption took place before the child became 16 years old. If you adopted the sibling of a child you already adopted, you must submit a copy of the adoption decree(s) showing that the adoption of the sibling occured before that child's 18th birthday.