Flowers, teddy bears and toy cars lay outside a family home in the Blue Mountains where two brothers were found dead.
Tributes to Russell Smith, 11, and his sibling Ben, nine, were propped against the fence of the Faulconbridge home as a photo of the smiling, dark-haired siblings was publicly released by their family.
The children were found by their father. Their mother, 42, remains in hospital under police guard.
The mother spent the night under arrest in hospital, where she was earlier taken in a stable condition. She has not been charged.
The father, who does not live at the Blue Mountains home, found the boys about 1pm on Tuesday and contacted police.
The mother's personal Facebook page is filled with photos of her and the children smiling together, showing them on frequent bushwalks and beach visits.
She was found injured inside the home along with their bodies, and was expected to be questioned by police on Wednesday, but confirmation of that has not been forthcoming.
Investigators have declined to speculate on what occurred before the brothers died but they are not looking for any other parties.
Premier Chris Minns said the "horrifying, very distressing" incident was another reminder of the difficult job of emergency service workers.
"I can only imagine what the father of those two boys is going through today and I want to assure him the people of NSW are behind him as he deals with the turning of his life upside down," he told reporters on Wednesday.
"(This) has obviously distressed the people of NSW and I want to assure them every help will be provided to the father of those two boys in the days ahead as he deals with this incredibly distressing situation."
Blue Mountains mayor Mark Greenhill said the loss of "two precious souls in the most awful circumstances" would affect the entire community.
"Now is a time to come together and remember these two beautiful children and their extended family whose grief must be unimaginable," he said on social media.
NSW Police Commissioner Karen Webb went to the local police station on Tuesday to support to her officers, noting that many had children the same age as the boys.
Clinicians and support officers were on hand for police, while the boys' father was also receiving support.
"The older and more experienced you get in this job, things like this still cut to the core," Ms Webb said.
"It's a tragic situation and certainly ... more will be known as the investigation unfolds."
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