South Australian police are set to return to a suburban factory in Adelaide’s south-west in the search for the missing Beaumont children, who vanished from Glenelg Beach in 1966.

9NEWS understands detectives are planning a dig at the New Castalloy factory at North Plympton in the hope of either confirming or ruling out a theory the three siblings were buried there shortly after their disappearance.

Police first dug at the site in 2013 after details of the theory were published in a book titled The Satin Man .

The Beaumont children vanished on Australia Day, 1966.

Prior to their disappearance, the children were spotted by several members of the public.

Harry Phipps became known as the "Satin Man". (9NEWS)

The book outlined a case against a man, later identified as deceased businessman Harry Phipps, who was referred to as the “Satin Man” due to his apparent fetish for wearing satin clothing.

One of the book’s authors, Alan Whiticker, said Phipps’ own son accused him of killing Jane, 9, Arnna, 7, and Grant, 4.

“The (Satin man’s) son came forward to us and said he did see the Beaumont children the day they disappeared,” Mr Whiticker told 9NEWS in 2016.

An author of the book "The Satin Man" said Harry Phipps' son believes his father killed the Beaumont children.

“They came into the backyard of the family home, which is no more than 500 metres from where they were last seen.”

Two other potential witnesses have claimed they'd dug a hole for Mr Phipps at the factory, which he owned at the time.

The Adelaide Major Crimes Squad has revealed a new dig will take place at the site after state-of-the-art technology discovered an anomaly beneath the ground - showing disturbed earth where the children might have been buried.

Jane 9, Arnna, 7, and Grant, 4, have not been seen in 52 years.

A previous dig at the site in 2013 did not find any evidence. (9NEWS)

When police searched there unsuccessfully in 2013, they were questioned as to why they dug in one small area and were accused of ignoring information from the two men who claimed to have dug the hole.

“The men weren't present when the police dug a very small section of the factory and we would have liked them to have done a little bit more extensive excavation and perhaps had these men on board to say what exactly happened 40 years ago,” Mr Whiticker said.

9NEWS understands that since that search, police have been provided with new information which supports claims that another area of the property needs to be explored before the theory can be either confirmed or laid to rest.

SA Police conducted an extensive search for the Beaumont children at the time of their disappearance.

Mostyn Matters, a retired detective who worked on the case, has today told 9NEWS the theory needs to be fully investigated.

Former police officer Bill Hayes revealed to A Current Affair that he spoke with Mr Phipps' son shortly after the information was given to Mr Whiticker.

"He told me that his father was a pedophile. The description of his father fitted very closely to the description given of the man seen playing with the children. His father had a habit of handing out pound notes to children," Mr Hayes told A Current Affair .

"He told me he was taking them (the Beaumont children) to a place, a factory, that the father owned."

"His exact words were, 'they are in the sand pit, Bill.'"

The former sand pit is now a car park covered in layers of bitumen and concrete.

"We've only had flaky, cooky information. Here we have something much less than that, we have something that does seem to have substance," Mr Hayes said.

Police are yet to reveal when they will return to the factory.