Police said a 34-year-old woman had been taken to hospital with stab wounds and was stable.
The house in the Manoora suburb has been cordoned off and detectives are searching the yard.
Police have said it was a "tragic event" but there was no cause for public concern.
Queensland Police said in a statement earlier that they were called to a residence in Murray Street at 11.20 local time following reports of a woman with serious injuries.
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Queensland Premier Campbell Newman said he was "deeply saddened and shocked" by the events.
Police have not made any arrests, but said the injured woman was assisting with their investigations.
Specialist police officers were travelling from Brisbane to assist with the investigation, Detective Inspector Bruno Asnicar said, describing the incident as "extremely distressing".
Asnicar said he was unable to confirm the relationships between the victims.
But a relative told the police that the children were all siblings. She said the woman was their mother.