Kyle Seitz drove his car 3 times, not noticing that his baby son was dead in the back.

A baby has died after his dad drove the family car three times over the course of a day — before noticing the 15-month-old dead in the back seat.

US man Kyle Seitz allegedly forgot to drop off his baby son Benjamin Jacob Seitz at day care on the way to work on 7 July, after missing the turn-off to the infant’s daycare and stopping off to get coffee on the way to work instead, according to FoxCT.

Software programmer Seitz later drove to get lunch without noticing his son in the car, the arrest warrant indicates.

After work, Seitz went to collect his son from day care —  only to be told by staff that Benjamin — or “Benjabear”, as his parents sometimes called him — had not attended that day.

The warrant says Seitz then “walked out heading to his car in the parking lot and began walking faster”.

He found the motionless body of his son in the rear-facing carseat in the car’s back seat, The Courant reports.

NY Daily News reports that the state’s medical examiner’s office ruled in August the death was a homicide, caused by hyperthermia.

Seitz turned himself in to police this week after learning there was a warrant for his arrest and has been charged with criminally negligent homicide.

Seitz’s wife Lindsey Rogers-Seitz — who has said she believes it was a tragic accident, according to news.com.au — has written about her grief over losing Benjamin on a blog called The Gift of Ben.