Itmam-e-Hujjah And The Neighboring Eight Empires
Children are exempted, of course, the women were not killed as well, because it was not necessary. It was understood that without their men, they would not survive without coming into the fold of Islam. This was a social construction of that time.
It was not allowed to enslave the polytheists. Islam doesn’t allow to accept Islam. The history tells that all were grew up Muslims and women didn’t show anything rebellious. In fact, Islam’s invitation to to worship One God of their forefather Ibrahim and to condemn idolatry was quite acceptable but their men were an obstacle due to their chiefs. Once that obstacle removed people found no hesitation to accept Islam.