The relevant parts:
In April 2010, U.S. President Barack Obama placed al-Awlaki on a list of people whom the U.S. Central Intelligence Agency was authorized to kill because of terrorist activities.[32][33][34] The "targeted killing" of an American citizen was unprecedented. Al-Awlaki's father and civil rights groups challenged the order in court.[32][34][35][36] Al-Awlaki was believed to be in hiding in Southeast Yemen in the last years of his life.[26] The U.S. deployed unmanned aircraft (drones) in Yemen to search for and kill him,[37] firing at and failing to kill him at least once,[38] before succeeding in a fatal American drone attack in Yemen on September 30, 2011.[39] Two weeks later, al-Awlaki's 16-year-old son, Abdulrahman al-Awlaki, a U.S. citizen who was born in Denver, was killed by a CIA-led drone strike in Yemen.[40][41][42] Nasser al-Awlaki, Anwar's father, released an audio recording condemning the killings of his son and grandson as senseless murders.[43]
And US officials admitted the killing of the boy was mistake.