David and Wendy Farnell were speaking publicly for the first time since the story broke more than a week ago of seven-month-old baby Gammy, who has Down's syndrome and is being cared for by his surrogate mother in Thailand.
The couple told Australian television they felt they had little choice but to leave Thailand with Gammy's sister. "We wanted to bring him with us," David Farnell, 56, said.
They said they returned to Australia with Gammy's sister Pipah as the surrogate mother Pattaramon Janbua had told them "if we try to take our little boy, she's going to get the police and she's going to come and take our little girl and she's going to keep both of the babies".
The couple have been criticised for apparently rejecting the boy, who also has a hole in his heart and is being treated for a lung infection in a Thai hospital.
Ms Pattaramon said doctors, the surrogate agency and the baby's parents had known Gammy was disabled when she was four months pregnant but had not told her until the seventh month.
She said she had feared she would be asked to abort him but would have refused due to her Buddhist beliefs.
The Farnells said they were angry that the agency had not told them about the boy's condition until too late to safely abort. They said they want the baby. Public outrage intensified last week when it became known that Mr Farnell was jailed in 1997 for sex offences involving three girls aged under 13.