It’s the inability to differentiate between the suffering of the father and the suffering of the innocent child by the said deity that makes it unable to fit the definition of perfect justice, mercy and kindness. This is my personal disagreement that I am yet to find a satisfactory reconciliation for.
In my view, an innocent life was made to suffer greatly for absolutely no fault of its own. Fallen or not, the suffering of the child was wholly due to a said divinity inflicting it upon it. That is immoral, and unjust.
Reciprocal punishments are never just, because they are never equal in penalty. A life for a life is meaningless and unjust because it amounts to punishing the innocent. For the individual child that lost its life, what was its recourse? Another life? Remember, it too suffered unjustly. An eye for an eye, and the whole world will be blind.
I think if you would do a study of sin it might be helpful....God’s instructions are there to ‘protect us’ because no one knows the destructed course of sin as much as God does. which is why we are given the perameters of life and how we should live it.
Also a thorough study of David’s sin and why it was so grievious.
I do know that sin will always touch those in our life we most love though we foolishly think we can protect them from it. Comes to mind now..”Be sure your sin will find you out”.
In David’s sin there were many things which led up to that.. where He could have stopped the path he was on. In the end it cost two people their very life’s and positioned others to be part of the deception...who were also impacted. Let’s not forget the wife of the man David had killed...and what that ment to a woman in that time.
The list can go on but look closer at this...and how God views sin.
Below is a good place to begin in understanding the death of David’s son...perhaps this will help.
http://www.apologeticspress.com/articles/3400
Robert Ingersoll, 1876