Queen Athaliah of Judah allegedly killed several family members, possibly including children of hers.
Accounts of the life of Athaliah are to be found in 2 Kings 8:16-11:16 and 2 Chronicles 22:10-23:15 in the Hebrew Bible. She is usually considered to have been the daughter of King Ahab and Queen Jezebel of Israel.1 Athaliah was married to Jehoram of Judah to seal a treaty between the kingdoms of Israel and Judah, and to secure his position Jehoram killed his six brothers.2 Jehoram became king of Judah in the fifth year of Jehoram of Israel's reign (2 Kings 8:16). Jehoram of Israel was Athaliah's brother (or possibly her nephew).
Jehoram of Judah reigned for eight years. His father Jehoshaphat and grandfather Asa were devout kings who worshiped Yahweh and walked in his ways. However, Jehoram chose not to follow their example but rejected Yahweh and married Athaliah, the daughter of Ahab in the line of Omri. Jehoram's rule of Judah was shaky. Edom revolted, and he was forced to acknowledge their independence. A raid by Philistines, Arabs and Ethiopians looted the king's house, and carried off all of his family except for their youngest son, Ahaziah.
After Jehoram's death, Ahaziah became king of Judah, and Athaliah was queen mother. Ahaziah reigned for one year from the age of 22 (2 Kings 8:26) and was killed during a state visit to Israel along with Jehoram of Israel. Jehu assassinated them both in Yahweh's name and became king of Israel. He had Athaliah's entire extended family in Samaria put to death, ending the Omri dynasty in Israel.
Upon hearing the news of Ahaziah's death, Athaliah seized the throne of Judah and ordered the execution of all possible claimants to the throne, including the remnant of her Omri dynasty. However, Jehosheba, Ahaziah's sister, managed to rescue from the purge Jehoash, a grandson of Athaliah and Jehoram of Judah, who was only one year old. Jehoash was raised in secret by Jehosheba's husband, a priest named Jehoiada.
As "usurper queen", Athaliah used her power to establish the worship of Baal in Judah. Six years later, Athaliah was surprised when Jehoiada revealed that Jehoash lived and proclaimed him king of Judah. She rushed to stop the rebellion, but was captured and executed.
So it seems like Athaliah would have killed her grandson Jehoash if he had not beenhidden fromher. Thus she might possibly have killed any of her children that were available.
Eastern Roman Emperor Leo I (401-474) reigned from 457 to 474. Leo and his wife Verina had a son who died very young, and 2 daughters, Ariadne (c. 45-515) and leontia (457-after 479), and possibly a third daughter Helena who married Vakhtang I of Iberia.
Leo recruited a unit of Isaurian soldiers to counterbalance the too powerful Germanic soldiers under Asper. In 467 Leo married Ariadne to Tarasicodissa, leader of the Isaurians, who changed his named to Zeno. Their son was named Leo (c.467-474). In 471 Leo ordered Asper and his son Ardabur killed in the Great Palace.
Leo was appointed Caesar and heir to the throne in October 473. Leo I died 18 January 474 and Leo became Emperor Leo II, with Zeno as the regent for the young emperor. Zeno was appointed co-emperor with his son Leo II on 9 February 474. Leo II died on 17 November 474, leaving Zeno as the sole emperor.
His death having occurred so soon after he became emperor has led to speculation among some modern scholars that he was poisoned by his mother Ariadne so that Zeno could ascend to the throne. However no contemporary sources raised this suggestion, even though Zeno was unpopular, thus it is considered likely that Leo II's death was natural, especially when the high child mortality rate of the time is considered. Victor of Tonona, a 6th-century chronicler, says that Leo II did not actually die, but was rather taken by Ariadne and hidden at a monastery. This is very likely a confusion with Basiliscus, the son of the Byzantine commander Armatus. Basiliscus was crowned Caesar in 476 and was almost executed in 477 after his father was murdered by Zeno, but was saved by Ariadne. The confusion likely stems from the fact that Basiliscus was renamed Leo in order to avoid association with the usurper who rose against Zeno.
And those were the two examples I could think of when royal mothers might have killed their children.