A couple of things (and i'm just observing,so don't reply with any insults, please):
The pile of leaves could have been raked close to the garage door,forming a leaf "tent" of sorts The kids were probably small in size,and it is feasible that they could indeed hide in a pile of leaves.
Evidently, dad wasn't big on bagging,and the leaves were simply raked up and forgotten.He'd probably backed up to it,or over it,a number of times,and if it's in a damp area,they wouldn't hhave caught fire so easily.
He could have had his windows up & radio playing when he backed up,so he wouldn't hear the kids yell.Too many variables in this situation. Just a terrible tragedy.I pray the family can get through this.
you're reading an awful lot into it. the guy didn't think. he did a dumb thing. his kid paid the price. pray for both of them. but don't forget the other kid in the hospital.