DNA Testing, Used with Some Immigrant Visa Applications, Genetic testing is a useful tool for verifying a stated biological relationship when no other form of credible evidence is available in conjunction with an immigrant visa (IV) application

The IR-2 visa allows the child of a US citizen living outside the United States to lawfully enter and live in the country you don't need to inform the USCIS

Biology is not sufficient, nor is it necessary, The guiding law in your situation is likely INA 101(b)(1)(C):