California residents who are U.S. citizens and who wish to bring spouses, unmarried children under 21 or parents from a foreign country to the United States can do so under certain conditions. Those individuals can get a visa number immediately, but some other family members may be able to do so as well. Children who are married or over the age of 21 as well as siblings may also be able to get a green card.
The difference for these types of relatives is that they may have a waiting period before they can obtain a visa because the government only permits a certain number in this category to immigrate per year. This process can begin outside the United States or after an individual has arrived in the United States.
Inside the United States, the citizen sponsor must fill out a Form I-130 and then a Form I-485 after the I-130 is approved. From outside the United States, an individual can go through consular processing. This involves getting a visa based on Form I-130 and then traveling to the United States to become a permanent resident on entry.
Individuals interested in this process may wish to speak with a family immigration attorney, as this may help expedite the process and avoid errors. For example, if a 20-year-old woman is preparing to join her parents and she gets married, this changes her status and could delay her visa. On the other hand, if that woman did not marry but turned 21 before the visa processing was complete, she might still qualify to immigrate. The Child Status Protection Act governs this, and in general, a child's age at the time of application is considered the relevant age for determining status for immigration.
Source: US Citizenship and Immigration Services, "Green Card for a Family Member of a U.S. Citizen ", September 12, 2014