Generally it is true, U.S. citizen children ("sons/daughter") who are 21 years old or older can file an I-130 Visa Petition to initiate the immigration process.
HOWEVER, if the parent(s) is/are currently living in the U.S. without legal status after having entered the U.S. illegally, then the parent(s) will need to complete consular processing, which requires them to leave the U.S. If their visa is denied at the U.S. Consulate/Embassy abroad, the parent(s) may have to remain outside of the U.S. for months, years, or even for life.
If the parent(s) has/have or had been living in the U.S. for more than one year within the last 10 years without legal status then they will probably need to file a waiver, which requires they prove extreme hardship to their U.S. citizen or Legal Permanent Resident (1) Parent or (2) Spouse. Thus, if the parent(s) do not have a U.S. Citizen or Legal Permanent Resident parent or spouse, then they will not be able to immigrate to the U.S.
KEEP IN MIND: filing an I-130 Visa Petition does NOT guarantee that a parent is eligible to immigrate even if the Petition is approved. An I-130 Visa Petition approval basically only proves two things: (1) that the Petitioner is eligible to immigrate a foreigner, and (2) that the relationship between the Petitioner and foreigner is a qualifying relationship. It does not prove whether someone is ultimately eligible to immigrate to the U.S. It is possible for the government to approve an I-130 Visa Petition, but deny the green card, immigrant visa or Legal Permanent Resident application.
In summary, it is possible for U.S. children to immigrate their parents, but this is more common in situations where the parent(s) never entered the U.S. illegally. However, every immigration situation needs to be reviewed, because there are instances when a parent who entered the U.S. legally might still be subject to another ground of inadmissibility that would require a waiver or may not be waiveable. If the parent needs a waiver and doesn't have a qualifying relative to file it, then having a U.S. citizen child who is 21 years or older will not be enough for the parent to immigrate.
Filing an I-130 Visa Petition in situations where a parent is not eligible to immigrate could have any number of undesirable results such as:
(1) LOSS OF TIME & MONEY: After the Petition is approved, it can be canceled by the National Visa Center (NVC) if you fail to maintain contact with the NVC at least once per year after the Petition is approved and immigration visa (IV) processing begins. Thus, you could end up losing out on the money you spent to file it, and might have to file again and wait several months to years for another I-130 Visa Petition approval;
(2) VISA DENIAL AT THE CONSULATE: Parent(s) leave(s) the U.S. for their immigrant visa appointment and it gets denied, resulting in them having to remain outside the U.S. for months, years or even possibly forever; and/or,
(3) GETTING PLACED IN REMOVAL/DEPORTATION PROCEEDINGS: Parent's(') adjustment application gets denied, and they are placed in removal/deportation proceedings, which can result in them being ordered removed/deported.
Sometimes it is better to do nothing rather than something, but in every case it is a good idea to speak with a qualified immigration legal professional to discuss any immigration matter. There are many ways to immigrate to the U.S. and you should explore any viable option.
If you need legal advise about yours or any other immigration matter, call our office to schedule an appointment at 512-443-4788.