The United States family-based immigration is based on classification. Before the immigration service considers a person's immigration petition, a relationship must be established between the person and a U. S. citizen or a permanent resident. How soon the foreigner will be able to immigrate depends on whether his or her relationship is that of a parent, spouse, child, daughter, son, or sibling. In case you are wondering, immigration laws do treat the terms "child" and "son/daughter" differently. A child is an unmarried person under the age of twenty-one. If a person is married and under the age of twenty-one, he or she is classified as a son or daughter of a citizen or permanent resident. Similarly, if a person is unmarried but over the age of twenty-one, the term "child" does not apply. There is a significant difference whether a person is classified as a child or son/daughter child marriage. A child is considered an immediate relative of a U. S child marriage. citizen