Peter John Enright’s parents, Maureen and Michael Enright, didn’t report him missing when he disappeared in 1968 or 1969 aged three or four years old.

But police allege his mother Maureen, now 76, murdered him at their Brisbane home and may have had a hand in burying him in the yard.

“It’s been a fascinating case,” Detective Inspector Damien Hansen told reporters at the crime scene.

“There were 11 children in the family, he was number 4, a lot of those siblings were unaware (but) they’d heard stories.

“They were aware Peter existed.”

Detectives took Ms Enright into custody on Wednesday evening and charged her with murder after interviewing the surviving family.

Bone experts and forensic officers on Thursday started searching for Peter’s remains using ground-penetrating radar at the family’s Inala home, where Ms Enright has lived since 1966.

Peter was born June 17, 1965. His father Michael died in 2018.

“We’re searching for a body. We’re optimistic at this stage but that will be dependant on a lot of environmental factors … time and acidity of soils,” Det Insp Hansen said.

Homicide detectives started the murder investigation after receiving a tip-off in August about Peter’s disappearance and suspected death.

“A person came forward with the information,” Det Insp Hansen said.

Detectives have urged anyone who lived on Polaris Street in Inala in the 1960s and 70s to contact police if they have information.

“They were quite well known, some of the neighbours have been here for a long time too,” Det Insp Hansen said.

Ms Enright is scheduled to appear in Richmond Magistrates Court on Thursday.