When god commands the killing of children in the bible, is it because the children were pagan?

This is what the Lord of hosts has to say: 'I will punish what Amalek did to Israel when he barred his way as he was coming up from Egypt. Go, now, attack Amalek, .... Do not spare him, but kill men and women, children and infants, oxen and sheep, camels and asses.' (1 Samuel 15:2-3 NAB)