[Bob Loblaw]

"So what should my SIL have told my nephew about the truck with the bloody dead baby on the side? The one that he, in his little five year old mind, rationalized was going to kill his brother?"

Here are some suggestions for your sister-in-law to tell your nephew about the bloody dead baby:

"Sweetheart, no one is going to kill you or your little brother. Daddy and Mommy will protect you, because we love you so very, very much. That's what mommies and daddies do -- they love and protect their children."

[netmilsmom]

They said something like that.
The first night
The second night
The third night

and so on....