William Tyrrell inquest: Missing boy’s biological parents to testify

William Tyrrell's birth parents and the first NSW police officer to be on the scene when he vanished in 2014 are yet to give evidence at week one of an inquest.

The three-year-old was last seen wearing a Spider-Man suit in the garden of his foster grandmother's home. Source: AAP

The biological parents of William Tyrrell and the first police officer to respond to a frantic report the three-year-old had vanished are among witnesses yet to testify at an inquest into his disappearance and suspected death.

The boy's natural mother and father, who cannot be named for legal reasons, and Senior Constable Christopher Rowley are due to take the stand at the NSW Coroners Court as the first week of the inquest draws to a close.

William Tyrrell vanished from a home in Kendall, NSW in 2014. Source: AAP

His foster carers have already testified about the morning of September 12, 2014, when the boy was last seen in the garden of his foster grandmother's house in Kendall on the NSW mid north coast.

The woman called police at 10.56am and told the operator they'd been looking for William for 15 to 20 minutes.

"He was just playing around here. We heard him, and then we heard nothing," she said in the triple-zero call played at the inquest.

The foster mother described William as about two-and-a-half feet tall and wearing a Spiderman outfit.

"Mum's property is near a State Forest and they're on huge blocks. We've walked up and down ... and we can't find him," she said.

Sen Const Rowley saw the missing persons report and arrived at the property on Benaroon Drive at 11.06am.

He searched the house after more police arrived, and stayed with the woman as investigations gathered speed.

William Tyrrell disappeared from his grandmother's yard in 2014. Source: AAP

William was born to a mother and father "who were in a difficult relationship" and issues brought them to the attention of the Department of Family and Community Services, counsel assisting the coroner, Gerard Craddock SC, said on Monday.

He was a baby when he was placed into foster care in early 2012.

A massive search of nearby bushland and houses failed to find any sign of the missing boy. Source: AAP

The inquest continues before Deputy State Coroner Harriet Grahame.

Further hearings will be held across August when persons of interest are expected to be called to give evidence.