But Muhammad’s definition of a child was not the same as our modern understanding.  Following the surrender of the Qurayza stronghold, he ordered the execution of every male child who had reached puberty.  His men had the boys drop their pants so that they could chop the head off of anyone with pubic hair (Sahih Muslim 4390).

Keep in mind that many Muslims often insist that Aisha reached puberty at age nine, since that is the age that Muhammad began having sex with her.  If so, then the age for “manhood” among boys might have been considered around twelve.

Muhammad also played a bit loose with the lives of women and children during wartime.  As recorded in both Bukhari and Sahih Muslim:

It is reported on the authority of Sa'b b. Jaththama that the Prophet of Allah (may peace be upon him), when asked about the women and children of the polytheists being killed during the night raid, said: “They are from them.” (Sahih Muslim 4322, see also Bukhari 52:256)

This does not justify the targeted killing of women and children per se, but it does prove that collateral damage is entirely acceptable if it accomplishes the military goal of spreading Islamic rule.  It is doubtful that Muhammad would ever shrug off the killing of young Muslims as he did the killing of non-Muslim children.

Muhammad did, in fact, draw a distinction between Muslim and non-Muslim children and said that it would be permissible to kill a child who has no prospect of accepting Islam:

The Messenger of Allah (may peace be upon him) used not to kill the children, so thou shouldst not kill them unless you could know what Khadir had known about the child he killed, or you could distinguish between a child who would grow up to he a believer (and a child who would grow up to be a non-believer), so that you killed the (prospective) non-believer and left the (prospective) believer aside. (Sahih Muslim 4457)

After capturing Mecca, the prophet of Islam also ordered the execution of two “singing girls” who had mocked him in verse:

“…two singing-girls Fartana and her friend who used to sing satirical songs about the apostle, so he ordered that they should be killed…” (Ibn Ishaq/Hisham 819)