Henry Tran was being treated at The Children's Hospital at Westmead, after he was pulled from the knee-deep fishpond in the front yard of a relative's home in Fairfield West on January 2.

The boy remained in a critical condition in the hospital's intensive care unit for 10 days.

He died on Wednesday from his injuries, a NSW Police spokesman said.

Henry is the fifth toddler to drown in NSW, and the 20th person to have died in water-related incidents in NSW, since mid-December, a toll the Royal Life Saving Society has described as "unprecedented".

It is understood Henry and his family, from South Australia, were visiting the boy's grandmother, aunt and uncle in Sydney for the holidays when the tragedy occurred.

Neighbours on McGee Place reported hearing screams of 'Help! Help! Help!" coming from the house just before 10.30am on January 2.

Henry had fallen into the small fishpond in the property's front yard. His family were in the yard at the time and it took just minutes for him to disappear and fall into the water.

A neighbour, Ramsey Vong, took it in turns with one of Henry's relatives to perform CPR on Henry until paramedics and police arrived. The 33-year-old chef said he learnt resuscitation techniques by watching videos on YouTube and Facebook.

"I could see the water - a lot - come out of his mouth and nose," he said at the time.

"I wish for the New Year God takes care of him," he said of the little boy. "I wished I could do more."

In a separate tragedy on New Year's Day, two-year-old Vera Peacock drowned in a backyard pool in Macquarie Fields.

Just before Christmas, twins Robbi and Charli Manago, aged 23 months, were pulled unconscious from the pool of their Kellyville Ridge home. Charli died in hospital on December 26, while Robbi died three days later.

And 20-month-old Aria Dunn died after being pulled unconscious from the swimming pool of her family's house in Raby on December 11.