Most immigrant visas allow parents to bring unmarried children to the United States with them. Typically, the children need to be under 18 or 21 years of age, depending on the visa.
With Non-Immigrant Visas (for temporary visits to the United States), children must apply for their own individual visas separately. However, children under 14 years of age are not required to attend the in-person interview at the US embassy or consulate.
