Warning: This story contains upsetting details
Distraught family members have reacted to news that little Willow Dunn was allegedly left in a cot for two days after she died.
The body of the Brisbane girl, 4, was discovered by police inside a house in the Brisbane suburb of Cannon Hill on Monday morning.
Police allege Willow, who had Down syndrome, died on Saturday and lay dead for two days before paramedics were called.
Her father, New Zealander Mark James Dunn, 43, was later charged with her murder and allegedly said to police: "I'm in trouble, aren't I?"
News.com.au understands Willow's mother Naomi died during childbirth and that Willow temporarily lived with relatives before returning to the care of her father.
She and Dunn had another child, a boy now aged 7, who they celebrated in posts on Facebook.
In February, 2013, Naomi shared a photograph of the couple's first child. Next to it, Dunn wrote, "Love it".
In another photograph, he commented, "My baby boy xxxx".
Willow's half-brother shared a post on Facebook yesterday after learning of the tragic news.
"Rest in Peace Willow," he wrote. "It's so heartbreaking things have turned out this way, but you will forever be in our hearts. Fly high with mum."
A friend responded: "Your mum will be so happy to see her again."
Naomi died on November 5, 2015, while giving birth to her daughter. In photographs prior to Willow's birth, friends commented: "We just can't wait to meet her."
The Courier Mail reports Willow's stepmother, who has children of her own, told police she refused to care for the 4-year-old.
Court documents reveal the alleged murder occurred on or about May 23 at Dunn's home in Brent Street, which detectives cordoned off as they tried to determine the cause of death.
Police would not confirm the girl's cause of death or whether a post mortem examination has been completed.
Dunn did not appear in Brisbane Magistrates Court on Tuesday and has been remanded in custody to reappear in the same court later in July.
The Australian reports the little girl's face had been attacked by rats and that when paramedics arrived at his home, New Zealand-born Dunn asked them if he was in trouble.
Neighbours of the family told the newspaper they never knew about Willow.
"They've been there for that long and we didn't know a little girl lived there," one neighbour said. "I can't believe it."
Down Syndrome Australia issued a statement after the heartbreaking news.
"The (alleged) neglect or abuse of any child is not acceptable," Down Syndrome Australia CEO Dr Ellen Skladzien said.
"Children with disabilities, as any other children in the community, should be protected and cared for."
An online vigil for Willow was held around the country last night as Australians posted pictures of candles with the hashtag #HerNameIsWillow.
"I can't stop thinking about this little ray of sunshine, Willow Dunn, who should still be alive, should have been given the best chance to thrive," disability advocate and Order of Australia recipient Carly Findlay wrote on Twitter.
"Willow had Down syndrome. She's forever four."
Dunn will appear before a court on July 20.