Bokkie, 10, Matilda, nine, and seven-year-old Barney Robertson were reported missing on Thursday, police said.
The children sparked a nationwide search late last month when they disappeared after a weekend access visit with their father in the Blue Mountains, west of Sydney.
Six weeks after they disappeared, the children were found safe and well with their father, Murray Robertson, in a house in Launceston, Tasmania.
No charges were laid against Mr Robertson.
Police said Mr Robertson was not a suspect in the latest disappearance at this stage. The children's mother, Philippa Yelland, reported her children missing from an address in Wooloowin, in Brisbane's north, about 8am (AEST).
Australian Federal Police confirmed it was helping Queensland police find three missing children in Brisbane, but would not comment further.
More than a dozen state and federal police officers were at Ms Yelland's house this morning before beginning a door knock around the neighbourhood.
Uniting Church minister, the Reverend David Millikan, who accompanied the children's mother to Tasmania to pick up her children a fortnight ago"]I have spoken to both her and Mr Robertson this morning."She is frantic," Mr Millikan told the news.com.au website."And he's in a bad shape."
Mr Millikan said he would fly to Brisbane today to be with Ms Yelland.
Queensland police are to hold a media conference today.
Subsequent news item:
Brisbane's Robertson children have been found after going missing a second time, police say. Police spokesman Superintendent Colin Campbell said Bokkie, 10, Matilda, nine, and seven-year-old Barney Robertson were found safe and well at a town north of Brisbane after members of the public provided information. They were found with an adult male, who is being questioned by police. The children are now at a police station and will be reunited with their mother later today. Supt Campbell said the children's mother, Philippa Yelland, had noticed the children were missing when she woke early this morning. She then alerted police. Supt Campbell said no decision has been made on any charges, but the case was being treated as an abduction. Earlier, the father of the Robertson children said his kids had simply run away from home. Murray Robertson, responsible for the last disappearance, told National Nine News this morning he was nowhere near Bokkie, Matilda and Barney. In a voicemail message, he said the children might have run away because of a disagreement with their mother over a pet mouse. The children sparked a nationwide search late last month when they disappeared after a weekend access visit with their father in the Blue Mountains, west of Sydney. Six weeks after they disappeared, Mr Robertson contacted National Nine News, and the children were found safe and well in a house in Launceston, Tasmania. No charges were laid against Mr Robertson.