يُذَبِّحُ أَبْنَاءَهُمْ
He slaughtered their sons. (Al-Qaṣaṣ 28:4)
The act is attributed to Pharaoh. This need not mean he personally killed every child; his agents carried out the cruelty under his authority and command.
The action is assigned to its commanding cause or responsible ruler. This establishes responsibility and intensifies the moral force of the statement. Distinguishing the agent who orders from the individual who directly performs the act matters here.