"kill all the men and take women and children captive"

As per Islamic law (aka sharia), when muslims defeat any kafir in war, they are to do 2 things:
1. Kill all the men (by beheading, since that was the example set by Mohammed)
2. Take the women and children as slaves and distribute among the muslims

Prophet Mohammed himself started these practises, as recorded in the following Hadith:

Hadith Sahih Bukhari 5:59:512:
Narated By Anas: The Prophet offered the Fajr Prayer near Khaibar when it
was still dark and then said, "Allahu-Akbar! Khaibar is destroyed, for whenever
we approach a (hostile) nation (to fight), then evil will be the morning for
those who have been warned." Then the inhabitants of Khaibar came out running on
the roads. The Prophet had their warriors killed, their offspring and women
taken as captives. Safiya was amongst the captives, She first came in the share
of Dahya Alkali but later on she belonged to the Prophet.

Hadith Sahih Bukhari 5:59:447:
Narated By Abu Said Al-Khudri: The people of (Banu) Quraiza agreed to
accept the verdict of Sad bin Mu'adh. So the Prophet sent for Sad, and the
latter came (riding) a donkey and when he approached the Mosque, the Prophet
said to the Ansar, "Get up for your chief or for the best among you." Then the
Prophet said (to Sad)." These (i.e. Banu Quraiza) have agreed to accept your
verdict." Sad said, "Kill their (men) warriors and take their offspring and
women as captives." On that the Prophet said, "You have judged according to
Allah's Judgment."