South Australia’s most enduring cold case is set to be revisited, with police confirming a new dig site for the bodies of the missing Beaumont children.

Investigations into the 1966 disappearance of nine-year-old Jane, seven-year-old Arnna and four-year-old Grant have led detectives to an area at the back of an Adelaide factory.

A fresh dig at the North Plympton site, which was also excavated in 2013, is set to begin in the next few weeks, police say.

The Seven Network conducted it own investigations into the factory site.

“Channel Seven has made available to SAPOL results of geophysical investigations which in conjunction with fresh information from witnesses has led police to examine a new area at the rear of a factory, which is now Castalloy,” police said on Monday.

The Beaumont children failed to return from a trip to Glenelg beach on Australia Day more than 50 years ago.

The state government has offered a $1m reward for information leading to an arrest and conviction or the discovery of the victims’ remains.

Anyone who has fresh information about the case is asked to call CrimeStoppers on 1800 333 000.