Saffie Rose Roussos was attending the concert with her mother, Lisa, and her sister Ashlee Bromwich, aged in her 20s.
The Telegraph reports Saffie became separated from her family during the attack. Her mother Lisa is believed to be in a coma and does not know her daughter has died, while her sister Ashlee is recovering in a separate hospital from injuries she sustained during the explosion.
In a statement released after Saffie's death was confirmed, Chris Upton, the headteacher at Tarleton Community Primary School where she was a student, said the news was "heartbreaking".
"Saffie was simply a beautiful little girl in every aspect of the word. She was loved by everyone and her warmth and kindness will be remembered fondly. Saffie was quiet and unassuming with a creative flair," he said.
— Nine News Australia (@9NewsAUS) May 23, 2017