William's mum pleads: 'Let him come home'

The mother of missing Sydney boy William Tyrrell has made an emotional plea to the child's alleged kidnapper to let her son come home.

Three-and-a-half years after losing her boy in one of Australia's most high-profile missing child cases, a tearful Karlie Tyrrell has made a direct appeal to William's alleged abductor to return him unharmed.

"Don't hurt him. Just let him come home, please," she told the Seven Network's Sunday Night program.

"I feel like whoever has him needs a bullet."

Tyrrell's then three-year-old child was wearing his Spiderman costume while playing in his foster grandmother's yard south of Port Macquarie when he vanished in September 2014.

The 29-year-old has laid blame on William's carers, saying they should feel guilt over the tragedy.

"They were responsible for looking after him and they failed," she said.