Judge Geoff Rea told the court Ms Crous had lifted up her cell phone to see how far away she was from her destination. She took her eyes off the road for a couple of seconds, and when she looked up it was too late. She hit at full speed into the rear of a stationary vehicle.
Eight-year-old James Crous was wearing a seatbelt, but broke his neck and died at the scene.
Her 5-year-old daughter and an 11-year-old girl in the other car suffered cuts and bruises.
Her lawyer, Scott Jefferson, said the Crous family had relocated to New Zealand from South Africa for a better life. He described Ms Crous as a "doting parent" who home-schooled James.
Mr Jefferson said the serious crash investigation report highlighted that the signage around the work site, which reduced traffic to one-lane over the bridge, was a "little inadequate" given the 375-metre line of traffic on the northbound lane, Mr Jefferson said.
However "she ought to have seen it," he said.
Mr Jefferson told Judge Rea that the crash has been devastating for the family and Ms Crous is shattered by her own actions.
"The fact she has to live with her own actions is the ultimate penalty," he said.
Judge Rea told Ms Crous that her sentencing was among the most severe and difficult.
"The result of your actions has been horrendous for you and your family," Judge Rea said.
He said the very reason it is illegal to use a cell phone while driving is because of exactly what has happened. Paying attention to technology had led to a catastrophic result, he said.
In handing down a sentence of six months supervision, Judge Rea told the emotional mother that "any penalty is insufficient compared to the life-long penalty of the loss of your son".
Hawke's Bay serious crash unit officer in charge, sergeant Cory Ubels said his sincere hope was that it reminds others to put away their phones while driving.
"Behind every fatal crash like this there are family, friends and loved ones left behind grieving, and communities that are left that bit emptier through crashes that in most cases could have been prevented."
He said using a phone while driving wasn't worth risking this pain.
"The driver of the car crashed into is also suffering the ongoing effects of such a traumatic incident. It demonstrates how easily a moment of inattention can result in horrific consequences."
Mr Ubels said if people need to use their phone they should pull over safely or get a passenger to check it for them. Other innocent road users deserve people's full attention.
