Child protection advocates are demanding an inquiry after Gold Coast residents revealed they tried to get help for the baby of a homeless couple, months before the girl was found dead on a beach.

Two locals say they contacted police and other authorities months ago, raising serious concerns about the welfare of the nine-month-old and her toddler brother.

They told authorities the baby was sleeping rough near Surfers Paradise Beach, where she was found dead on Monday.

Gold Coast resident Erin Sorensen said she went to police two months ago, fearing for the baby and her brother, who was about two.

“It was winter and the dunes were freezing every time the sun went down. I didn’t think that was good for a baby or toddler,” she wrote on Facebook.

“I reported it straight away and monitored the following week. And if authorities did the job correctly this little girl would still be here!”

The baby’s parents – a man, 48, and woman, 23 – are in custody but have not been charged.

Another resident wrote to the Gold Coast City Council in May, expressing similar fears as the family spent winter nights sleeping on a wooden platform in a park. At night the baby could be heard crying.

“Why was the baby left with the parents, just why?” the resident, who was not named, told The Gold Coast Bulletin.

Council staff wrote back after five days, telling the resident to raise the matter with other authorities as it was not a council responsibility.

A support worker from homeless services did visit the family but the couple refused help, the Bulletin reported.

Child safety advocate Hetty Johnston said there must be a public inquiry into how the girl was left in such a heart-breaking situation.

“The public needs to understand the system they are paying for and how broken it is,” the Bravehearts founder said.

“If they (child services) did know about this family, we need to know what happened here. And if they didn’t know, then there’s something seriously wrong there.”

The young girl’s parents were already known to police. Queensland’s child safety department won’t say if it was aware of the family’s circumstances.

Queensland police declined to say what action was taken regarding Ms Sorensen’s complaint.

On Tuesday, Queensland Police Commissioner Ian Stewart confirmed the baby’s brother was being cared for and was safe.

Detectives are trying to determine if the baby was dead before she was found by a passer-by at the water’s edge. It’s believed she had been in the water at some point.

Meanwhile, NSW Police are looking at the couple’s movements in the Tweed Heads area, on the border with Queensland, where they were also known to have been sleeping rough.

Queensland police expect to receive the results of an autopsy on Tuesday.

-AAP