A man has been charged with murder 47 years after a toddler disappeared from a Wollongong beach while on a day out with her family.

Cheryl Grimmer was at Fairy Meadow Beach with her mother Carole and brothers Ricki, Stephen and Paul on January 12, 1970, when she vanished from near a toilet block.

Police allege the three-year-old was killed within an hour of being separated from her siblings.

A coronial inquest in 2011 ruled she had died, although her body has never been found.

Police formed Strike Force Wessel to re-investigate the case.

Detectives and Cheryl's brothers made public appeals for information in December 2016 and January 2017.

On Wednesday, police arrested a 63-year-old man in the Melbourne suburb of Frankston over Cheryl's disappearance and successfully applied to have him extradited to NSW.

The man, who cannot be named, arrived at Sydney Airport on Thursday wheeling a small suitcase and was met by waiting news cameras.

He remained silent as he was escorted through the terminal by detectives, before climbing into a car which took him to Wollongong police station.

In a statement, NSW Police said the man was then charged with murder, in "a major breakthrough in one of the state's longest mysteries".

He will face Wollongong Local Court on Friday.

Stephen Grimmer, who was five years old when his sister disappeared, will be at court to face Cheryl's alleged killer.