God wants all the women and little boys killed

Numbers 31:17 says, “Now therefore kill every male among the little ones, and kill every woman that hath known man by lying with him.

31:18 But all the women children, that have not known a man by lying with him, keep alive for yourselves.”  God wants his people to kill all the little boys and women but to take as slaves all the little girls.  What kind of god is this?