Instead, his mum Madelene handed him a teddy bear.

"I said Mum 'I'm too old for a teddy bear.' She said 'firstly, you're not. No one is. Secondly, it's not for you. It's a trauma bear, for any kid you think needs it'," he wrote in a Facebook post which has attracted more than 154,000 likes and 27,000 shares.

True enough, that small knitted bear would not remain in his truck for long.

Three months later, a little boy whose life was crumbling would take that teddy bear with him as he left the scream of sirens behind.

"There was a scared bear in my police truck that needed looking after ... while his world dissolved in sirens and lights that boy kept that bear safe and took him home," he wrote.

Mr Sweeney's mum has since knitted thousands of trauma teddies, booties for premature babies and even blankets for patients in drug rehabilitation, which he has dutifully delivered first as a police officer, and now a Canberra prosecutor.

He said in times of tragedy, upheaval or anguish, a teddy bear can tether you.

"People don't usually call the police with good news. Often people meeting you as an officer are having the very worst day of their lives. Handing over a trauma teddy to a little child whose life in that moment has come to a dreadful catastrophe is one of the best things I've ever done," Mr Sweeney said.

It takes Mrs Sweeney about two days to create one of her trauma teddies. She knits on the bus or while waiting for appointments, using a basic pattern and any colour wool you can imagine.

"They're not lovely things to look at but they're soft and cuddly," Mrs Sweeney said.

More important than the stuffing or the spools of wool is the love that goes into each and every stitch.

"You have to put that in otherwise they don't work," she said.

"You give them without strings attached, you give them as a gift of love. I've been known to give one I'd just finished knitting to a child on the train. It really works."

For her part, Mrs Sweeney has been completely overwhelmed by the response to what she seems an innocuous act of kindness.

She's also quick to point out there are many crafters around Canberra who also knit these items without the fanfare they deserve.

"It's just something that you do," she said.

Mr Sweeney said it can be powerful to know someone who has never met you cares, a special kind of "grandma magic".

"It's like you're getting a hug from a grandma you've never met. She's knitting something for you, she's putting time into making you something you can hold," Mr Sweeney said.

"I think if a police officer, a nurse, or someone who's caring for you goes a little further by handing you something [like this], it's proof that you are loved, that someone gives a damn. I can promise you my mum gives a damn. My mum has a lot of love to give."