Joshua 6:21

‘ And they devoted (utterly destroyed as an offering to YHWH) all that was in the city, both men and women, young and old, and ox, and sheep, and ass, with the edge of the sword.'

Warfare is ever a dreadful business. Even practically speaking they dared not leave men alive in their rear who could attack them from behind when they went on. And to leave the women and children alone and undefended would have been unacceptable. death would be seen as preferable. But here Jericho was the firstfruits of their inheritance, and therefore dedicated to YHWH. And they were carrying out God's judgment on the particular wickedness of the Canaanites, their debased idolatry and their sexual perversions, wickedness which if it was not destroyed would in the end prove harmful to them (as later it did). None could be allowed to live. They were under the judgment of God. The slaughtering of the animals, which they would have liked to keep, demonstrates that it was not just blood lust.