Through this information, we find that the only people under the command to be killed are those who are a part of the invading army.
If that is so, then why were women, children and infants included?
Women - up until relatively modern times, packs of women followed armies. These women would support the army: cook, clean armor, provide sexual favors (prostitutes historically made up a significant number of these women). They, like the invaders, were hoping for a portion of the wealth attained during the invasion. Usually, these women were not wives, as they were usually left at their homes to take care of the homestead while their husband brought back the spoils of war. So, the women involved in the army would have been just a much a part of the invasion as the soldiers who fought.
Children - children fought during this time too. Mainly they were used for auxiliary tasks like providing arrows to archers and running messages, but they also fought from time to time. Common practice amongst the Israelites was to spare the children in battle if possible and absorb them into the army. We can see evidence of this with David working in Saul’s army with his three eldest brothers. In an invading army, we see a different situation than David’s. Saul’s army was nearby and thus, he joined the army to help defend his home. The children in the Amelekite army left their home specifically to be part of the invasion.
Infants - These would be the children, usually born out of wedlock, to the soldiers by means of the prostitutes following the army. To our modern eyes, they are innocent. To the Jews of the time, however, they were products of the invasion and defilement of the Promised Land. As such, they couldn’t be taken into the tribes of Israel, even as slaves. The infants resulting from the rape of the native Kenite women would not be included in the slaughter, as they would be considered Kenite, not Amelekite. Only the children resulting from the willful coupling of an Amelekite woman with an Amelekite soldier would be included.
That being said, we don’t even know if any infants were actually present to be killed. “…kill men and women, children and infants, oxen and sheep, camels and donkeys.” This is a ritual phrase simply meaning “Kill everyone” and in this context, “kill everyone in the invading army”.
The hardest part for modern readers of the Old Testament is to immerse ourselves in the theological meaning of the time and see it in the light in which it was originally written. We cannot read into Scripture modern interpretation.
Hope this helps.
God Bless,
Br. Ben, CRM