When defending the genocides of the Old Testament, the most common approach is to say that the children/infants who were killed were born sinners, and therefore deserved death, and in fact we all share that condemnation, thus we should be glad God is not killing or torturing us this very second.
Why is every child that is born already sinful, apart from doing anything?
Why are all people sinful?
Who made them that way?
Where does that sinfulness come from?
Is it fair for children to be born with guilt for something they may not want?