According to 7News, a man is currently in custody in Castle Hill following the attack.
The minor was rushed to Westmead Children's Hospital under police escort, but sadly he could not be revived.
Furthermore, his 60-year-old grandmother was treated for shock at the horrific scene.
The news site also reports that the 36-year-old man has a relationship with the child, but no further details have been confirmed.
This is a developing story.