The sound of silence fell on the front yard of a home in a quiet cul-de-sac street in Kendall.

It was that moment William Tyrrell's foster mother was consumed by a feeling of dread.

Day two of the coronial inquest into the disappearance of William Tyrrell continues in the NSW Coroner's Court today (March 26).

The week-long proceedings will hear evidence from William's family about the first crucial moments after the toddler went missing in September 2014. He has not been seen since despite an intensive investigation by a strike force of police detectives.

On Tuesday, William's foster mother told the coroner she immediately thought "someone has taken him" in the moments after he disappeared from his grandmother's yard in Benaroon Drive where he had been playing with his sister.

"I couldn't hear a thing. It was silent, there was no wind, there were no birds," she said.

Counsel assisting the coroner, Gerard Craddock SC, asked: "In your experience, that little part of this little village, sound carries pretty well?"

"Oh, unbelievably. You can hear everything," the foster carer replied.

She said she was left standing in the backyard of her mother's house wondering why she couldn't hear William or see him in his red Spiderman suit because "it hasn't been that long".

He'd been playing "daddy tiger" and roaring at the two women.

"My immediate thought was somebody has taken him and he's gone," she said.

The woman, who cannot be identified, had a blue-and-red "Where's William?" ribbon pinned to her chest as she sat in the witness box giving evidence.

On Monday, she testified having seen three cars on the street the morning he disappeared - including one white and one grey car parked between two driveways.

The woman on Tuesday said she didn't realise until after William went missing that those two cars were gone.

"I know in hindsight that they weren't there but whilst I was searching I didn't. In the initial stage, it didn't even occur to me that those cars weren't there," she said.

Mr Craddock said he expected the evidence before the inquest would establish William "was taken" and his disappearance "was the direct result of human intervention".

The first week of hearings will explore William's foster and biological families, when he disappeared and the action taken shortly after he went missing.

Family members, neighbours and police will give evidence.

Further hearings will be held in August when persons of interest will be called to testify.

Strike Force Rosann, the team charged with gathering thousands of pieces of evidence, has been led by Detective Chief Inspector Gary Jubelin.

In that time, there have been more than 600 persons of interest detectives have had in their sights.

Those profiles may include only physical descriptions from suspicious sightings and information gathered by police.

Some were charged with unrelated crimes as detectives dug into their pasts, others were cleared entirely.

Other teams at NSW Police's State Crime Command, home to the force's elite squads, have also assisted with the investigation.

In 2015 it emerged a ring of pedophiles had been active in the area and were being investigated. Years later, that theory has not conclusively been ruled out.

Under the powers granted to the coroner, persons of interest may be forced to explain their movements and knowledge of William's disappearance before the court.

A $1 million reward remains in place for information that leads to the return or recovery of William Tyrrell. It is one of the biggest rewards on offer in NSW.

At the time, Premier Mike Baird said the abduction of the then three-year-old on September 12, 2014 tore the family and the Kendall community apart and touched the hearts of people across the nation.

"What we need to do is everything possible to bring William home," Mr Baird said as he paid tribute to the Strike Force Rosann team.

"It's an incredibly difficult thing to watch as a parent. Every parent across the nation sits and is absolutely in the sense of deep grief with that family as we think about these terrible, terrible circumstances."

The inquest before Deputy State Coroner Harriet Grahame continues.