My aunt's child (my sister) got a green card in America, and her brother-in-law is American. How can my children go to America?

Your aunt's children are commonly called cousins, and there is no such level in the definition of "kinship" in the United States, so they will not help your children go abroad. At best, it is to provide financial assistance, and this can't be told to the visa officer, otherwise it will easily be judged as "immigration tendency". Supplementary answer: To adopt a child of one's own siblings, it is necessary to obtain the conditions that the child is an orphan or the parents are incapable of raising, and it is necessary to go through the adoption procedures. This child is divorced from his parents and can't sponsor his biological parents to immigrate in the future. After becoming an adopted son, the child can apply for family reunion immigration as an adopted son. China Adoption Center specializes in foreign-related child adoption services. The adopter is limited to over 30 years old and has strict requirements on economy, physical condition and moral conduct. The adopter can only adopt one child at a time (except twins), and report the living conditions of the child once every six months until the child is naturalized. Overseas adoption is a very complicated legal procedure, which not only conforms to the immigration law and the relevant provisions of the adopter's country of residence, but also conforms to the legal requirements of the child's country of birth. If the adoption is not carried out in accordance with the laws of the country, then the child is not eligible for immigration. If you are considering adopting children to immigrate (note: only children can immigrate, and you have no right to immigrate as a biological parent), it is best to consult an immigration lawyer with experience in this field.