Chris died at the scene of the crash.
Life support for one-year-old Jack was turned off on Friday morning. He died later that day.
On Friday NZ Bus chief executive Zane Fulljames said the company was devastated by the news that Jack had passed away.
"We are all shattered and devastated by the passing of baby Jack this morning and the death of his father Christopher, and offer our deepest condolences to the family and their loved ones," he said.
"We extend our support to the family and continue to support our driver to ensure their wellbeing following this tragedy. We fully co-operate with the police to assist in their investigation."
Jack's 2-year-old sister Elle is in a stable condition in hospital.
The crash happened just minutes from the family's Mt Eden home.
A Givealittle page has been set up to raise money for his Chris' devastated wife Olivia and their children. It has raised more than $24,000.
Tobin is suspected to have suffered a medical event before the crash on the corner of Mt Eden Rd and Bellevue Rd.
His car crossed a median strip and collided with a double-decker bus.