The Hutt Valley District Court was told how the "bouncy 5-year-old" was in the habit of riding on the rear bumper of the van while the father slowly drove back to the house, after helping him empty the day's rubbish into the skip at the rural property where they lived.
On January 16 last year, he slipped and fell - but his father believed he had jumped off as usual and started reversing.
He only realised what had happened when he found his son under the vehicle.
The child died at the scene.
The father later pleaded guilty to careless driving causing death.
He and his partner wiped away tears as her victim impact statement was read aloud to the court by her sister.
She said her son "used to say he wanted to be just like his dad" and she knew "that would still apply".
"Our life has been turned upside down - and the charges have added to nightmare. We have suffered and continue to suffer a life-long sentence."
The mother described her partner of 10 years as a loving, hands-on parent.
Despite his grief, he had continued working hard at his business since the accident to support his family, as well as having counselling.
The man's lawyer, Shane Robinson, asked for him to be discharged without conviction "on compassionate grounds", saying while the outcome was "most serious, the action was not".
He argued his client should not lose his licence, which he needed to run his business and look after his family.
Police prosecutor Wilber Tupou said the Crown did not oppose permanent name suppression, and also accepted there was no need to disqualify him from driving, as there was no risk to the public.
However, he argued the threshold for discharge without conviction was not met.
Consequences "were not out of proportion to the gravity of the offending" and there was no indication a conviction would "prejudice him in his line of work".
However, Judge Barbara Morris discharged him without conviction, calling the situation "a tragedy".
Explaining her decision, she said the consequences were "out of all proportion to his low culpability; in other words, it would cause more harm than good".
"Nothing the court can do can in any way affect what he and his family have already gone through."
She said the Crown maintained there was "medium culpability" involved in this case, but the father could take comfort from the fact that many parents would have done similar things.
"I hope that you and your family can get on with your life in the knowledge that your young son would be proud of you and everything you have achieved for the benefit of your family."
