The three-year-old, dressed in a Spider Man outfit, vanished while playing in the garden of his foster grandmother's home in Kendall shortly before 10.30am on September 12, 2014.

Within hours, hundreds of local residents and emergency service workers combined to search the rural community, looking in scrub, creeks and paddocks for William.

Police formed the view the disappearance stemmed from human intervention, and in March 2019 an inquest started into William's disappearance.

It remains ongoing.

Detectives are continuing to conduct interviews, searches and other investigative activity, including those under coronial orders, as well as reviewing all available materials with the assistance of various experts.

Detective Chief Inspector David Laidlaw said the Strike Force Rosann team returned to Kendall to have another look at the home where William was last seen, along with other areas nearby.

"Further information has since come to light, as part of our ongoing review of the materials gathered by investigators since the moment William went missing seven years ago," the strike force officer-in-charge said in a statement on Sunday.

"As our team continue to conduct inquiries and explore all avenues of investigation, our focus has been identifying if anything has been missed, or if there are any details - no matter how small - that need to be clarified.

"Police remain committed to finding out what happened to William, but our most important job here is to bring him home for both families."

In September 2016, the NSW government announced a $1 million reward for information that leads to the recovery of William, which remains on offer.

Australian Associated Press