The baby did not know what religion meant.
The ISIS Sunni gunmen knew about the baby, they knew he was a Shia or an Armenian Christian.
The baby did not know what he was.
He could not answer to their questions.
The gunmen was almost sure the baby’s parents were not Sunnis.
What should be done?
Kill the baby.
The baby did not know why he should be killed.
I do not know what happened there. I am only guessing.