If the boy was present at the scene because the 4-year old girl corroborates grandma’s story, it’s not that tough to fool a 4-year old! Boy already dead grandma says ‘he’s sleeping’, etc.. Then she hides boy’s dead body back at the car and tells girl ‘he’s missing’, etc.. ELABORATE HOAX BY GRANDMA!
I thought of that also.Could be anything. I am thinking an accident and coverup.