William Tyrrell's foster parents have been charged with fraud.

The 55-year-old man and 57-year-old woman, who cannot be named for legal reasons, allegedly had someone make fake bids on a house in Sydney at auction.

The offences allegedly took place between December 10 and 12, 2020.

They have been charged with with dishonestly obtaining financial advantage by deception, and are due before a court in Sydney in October.

The maximum penalty is 10 years in prison if convicted.

The charges are unrelated to William's disappearance. He vanished from his grandmother's home in Kendall, on the New South Wales mid north coast, in 2014 when he was three years old.

No one has been charged over his disappearance.