Experts have begun excavating an Adelaide factory carpark today following a fresh lead in the search for the missing Beaumont children.
A big police presence is currently at the North Plympton site that is the focus of renewed investigations.
The dig is expected to continue for at least several hours on Friday.
The children never returned after leaving their parents' Glenelg home for an afternoon at the beach on Australia Day, 1966.
Their disappearance sparked a wide-scale search operation, but nine-year-old Jane, seven-year-old Arnna and four-year-old Grant were never found.
In 2013, new information focused the investigation on a factory west of Adelaide, after two brothers told police they spent the 1966 Australia Day weekend digging a large hole there at the request of owner Harry Phipps.
Phipps died in 2004, but his son, who accused his father of years of sexual abuse, believed he had a part in the crime.
He also bore a resemblance to an identikit picture prepared at the time, and lived close to Glenelg Beach.
This is the second excavation at the North Plumpton site, after the first proved fruitless. Recently, police worked with experts using new technology surveying the site. Today they are investigating an anomaly in the soil which matches the size, shape and site the brothers claim they dug a hole.
A range of experts will be present on Friday while the site is dug up, including a forensic anthropologist, a criminologist and officers from the major crime division.