Like United States Citizens, Lawful Permanent Residents (LPR’s) may petition for their unmarried adult sons and daughters. However, unlike United States Citizens LPR’s are not eligible to file for their married children.
Be aware, that the process can take many years under the family-based 2B category as the number of people who are allowed to immigrate under this category are extremely limited. Furthermore, due to per-country limitations, those seeking to emigrate from a high immigration country face significant wait times of several decades or more..
However, if the Petitioner later naturalizes and becomes a US citizen, their unmarried adult sons and daughters will retain the priority date of the 2B visa petition and will automatically convert to the 1st preference category (unmarried adult sons and daughters of US citizens).
If the wait under the 1st preference category turns out to be longer, the Child Status Protection Act (CSPA) permits your son or daughter to “opt-out” of the conversion, and return to the 2B category despite the fact that you are now a US citizen.