Former Wallabies hooker Brendan Cannon says he'll be forever haunted by the thought he could have killed his youngest son.

Cannon reversed his four-wheel drive over his 16-month-old son Samuel in the driveway of the family's Sherwood home in Brisbane's southwest on Saturday.

Paramedics had feared Samuel would die, but he's making steady progress in Brisbane's Royal Children's Hospital and Cannon says the latest prognosis is a full recovery.

But the little boy has a lot of healing to do. Both of his legs were broken and he also suffered internal injuries.

His lower body is in a cast stretching from under his ribcage to his toes.

"Every day that Sam has recovered, and has shown such amazing resilience and positive steps ... has helped me," Cannon told reporters at the hospital on Wednesday.

He said he'd spoken to former Wallabies captain Phil Kearns, who in 2005 accidentally reversed over his then 19-month-old daughter Andie at the family's Sydney home.

"I have spoken to Phil Kearns. His daughter has recovered fully but he says he still thinks about it every day and I think that will be the circumstances for me," Cannon said.

"But the fact that the prognosis at the moment is that Sam's going to make a full recovery is magical for me."

Samuel had been playing with his mother Fiona in the back garden when he suddenly ran over to the car after seeing his siblings Joseph, five, and Phoebe, three, getting into the vehicle.

His mother Fiona said the accident happened in the blink of an eye.

"Brendan was just going to bolt up to the shop and get some buns for the kids. ... I was hanging out the washing and Sam was with me," she said.

"... I turned around and he wasn't there and (then) Brendan was carrying Sam.

"Literally, it felt like a second."

She said both Joseph and Phoebe witnessed the accident, but Joseph comprehended more and was not coping as well as his sister.

Orthopaedic surgeon Dr Trevor Gervais said Sam had the advantage of youth and was healing well.

He said he expected the cast would come off in six weeks' time.

"We expect from his orthopaedic injuries he will make a complete recovery," Dr Gervais said.

"I don't see this affecting how he will walk and function later down the track. I expect he will be able to do all the normal activities he would want to."

Cannon's message to parents is to not take their eyes off their children.

"You've just got to make sure you see your kids all the time," he warned.

"It happens in an instant."

He said the accident happened despite a reversing camera being fitted to his vehicle. He said there may be a need for a new awareness campaign.

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