The immigration law defines a child as an unmarried person under the age of 21 (a minor) who is:
 
•A child born to parents who are married to each other (born in wedlock)

•A stepchild if the marriage creating the step relationship took place before the child reached the age of 18

•A child born out of wedlock (the parents were not married at the time the child was born). If the father is filing the petition, proof of a bona fide (real and established) relationship with the father must be supplied

•An adopted child if the child was adopted before the age of 16 and has lived with the adoptive parent(s) in their legal custody for at least twoyears 

•An orphan under the age of 16 when an adoptive or prospective adoptive parent files a visa petition on his or her behalf, who has been adopted abroad by a U.S. citizen or is coming to the U.S. for adoption by a U.S. citizen

•A child adopted who is under the age of 18 and the natural sibling of an orphan or adopted child under the age of 16, if adopted with or after the sibling. The child must also otherwise fit the definition of orphan or adopted child