One of the challenges to Christianity concerns the description in the Old Testament of the complete wiping out of several nations - including women and children. I thought it would make sense to comment on these accounts briefly.
Firstly, in broad terms I agree that you can't read the accounts of "ethnic cleansing" in the Old Testament without finding it shocking. However ...
... those people whom God ordered the Israelites to slaughter in Joshua - did they have the chance to defend themselves? Yes - and it seems unlikely that the population of a city would be less able to defend itself than a nation that had spent 40 years wandering in a desert. Did they have the chance to agree terms with the Israelites? Yes, in many cases. Would they have spared the Israelites had they managed to beat them in combat? Probably not - check out the military behaviour of some of the other nations of the era - no Geneva Convention then. Did God explain why he asked the Israelites to act against the people? Yes. Did God explain why they should be totally destroyed? Yes.
Does anything in these accounts suggest that what happened at that time could be more generally applied to any other historical context? A resounding NO!
Given that God (if he exists) ushers tens of thousands of people out of this life every day, do you think that "normal, everyday" God is less culpable than "special revelation" God? Presumably not.
Given that (according to the Bible) God gives life as and when he chooses, do you not think that it is within his remit also to take it as and when he chooses?