Police said Ms Blencke had "done everything right" before the accident, which occurred at Rushcutters Bay on Wednesday morning.
Ms Blencke had watched to see Harry, three, and his elder brother Christo walk up the road with their father before she reversed.
But it is believed Harry darted behind the car in chase of a soccer ball.
"The pain is unbearable," Ms Blencke said.
"We thank everyone for their love and prayers and we hope this never happens to another family again."
Oh Dear Lord.....How tragic.....such a tremendous Loss....What a beautiful Child...The Child has been released into the hands of the Divine.....MOM.....Has to live with this....No Mother should EVER have to endure this.....Dear me ....this is so sad. SOON they will be reunited in Grace...
I am sending all the Angels and Prayers to this Family, what can i say, nothing, nothing in the world is worth than a loss of a Child. i Pray for them and for all the Families around the world who live the same tragedy. we are one, All the Children of the World are our Children, All the mothers are us, all the Fathers are us