Why in hell would they execute a 7 month old child whilst making a getaway, just for fun???
My guess is the Dad had been followed by the thugs to that house. He wasn’t there to “visit,” but to do some quick business while at the door, which is why he left the baby in the car instead of bringing him into the house. The killers wanted a piece of that business and helped themselves and left a message that no one was to conduct such business in that area without including them in the proceeds.
A vicious gang had a reason for this brutality. Shocking cruelty serves a purpose. Saddam and family knew this.