Why did God specifically mention the Children of Israel in His verse: "Because of that, We decreed upon the Children of Israel..." after the story of Adam's two sons, given the long period of time separating the two events?

The son of Adam was the first to establish killing, and the Children of Israel followed his example, killing prophets and attempting to kill one another. Allah forbade killing in all divine messages. The first book in which a warning against killing was mentioned was the Torah, due to the tyranny of the Children of Israel and their shedding of blood. And His saying, "Because of that" [Quran 5:32], could mean it is a continuation of the preceding discourse, or it could be a new discourse pointing to the corruptions resulting from killing, and that the obligation of retribution (qisas) is general in all religions, but the severity towards the Children of Israel was due to their audacious acts of killing prophets.