Justifying the slaughter of the Canaanite children by citing the alleged Canaanite practice of child sacrifice is a remarkably absurd line of reasoning

The argument assumes that both theists and atheists can understand that sacrificing one's children in state-sanctioned mass ritual executions is wrong. I can agree, that sounds pretty bad.

Problem: Canaanites are sacrificing their children.

Solution: Kill their children.

It almost sounds like a comedy skit. But from a theistic perspective, it gets even worse.

A common apologetic I hear as to the slaughter of the Canaanite children/infants is that they were simply being "moved" to heaven. Unlike their parents, they hadn't done anything wrong, and so the righteous Hebrew warriors were simply giving them a fast pass to heaven. I hate to point this out, but:

They were already going to heaven because they were being killed in ritual sacrifice.