Beaumont children mystery less likely to be solved as time goes on, Grant Stevens says

Grant Stevens says solving the case "becomes more difficult with the passage of time". (ABC News: Che Chorley)

The likelihood of solving the case of the missing Beaumont children — one of South Australia's most enduring mysteries — lessens every year, the state's police commissioner says.

Jane, nine, her sister Arnna, seven, and their brother Grant, four, were last seen leaving their beachside home at Somerton Park for a day at Glenelg Beach on January 26, 1966.