South Australian murder detectives are investigating a new lead about the missing Beaumont children almost 50 years after their infamous disappearance.

Jane, who was nine, seven-year-old Arnna and four-year-old Grant Beaumont went missing on Australia Day, 1966 after failing to return from a trip to Glenelg beach.

Missing Beaumont children Jane, Grant and Arnna.

Major Crimes Detective Superintendent Des Bray says police have never closed their investigations and are currently looking into a new lead involving a now-dead suspect.

But there's every chance it could come to nothing, like hundreds of other tip-offs about the children received over the years.