The irony was the 12-year-old knew how to swim.

With swimming and playing games in the pool a part of the quintessential Australian childhood, Jack's family wants to use the 10^th anniversary of his death to warn others.

For the past decade, Jack's aunty Sharon Washbourne has been raising awareness about the silent killer that every parent should know of in the hope that no one has to go through what they did.

"Shallow water blackout - that's what happened to our Jack," Mrs Washbourne said.

"Jack had been doing what you call no-breathers, they're laps without taking a breath and probably within a minute or so of having done a number of laps he said to his mum - 'mum watch me hold my breath one more time' and got into the shallow end of the pool."

Jack's mum, Michelle Ferrara, was sitting by the pool in NSW's Illawarra region with her six-month old baby in her arms when she realised something was wrong.

"She yelled out and he didn't respond so she called for help. Her daughters came and took the baby and Michelle jumped into the water, got him and started CPR right away," Mrs Washbourne said.

With shallow water blackout or hypoxic blackout, Mrs Washbourne said the only way to effectively save someone is to pull them out of the water straight away.

Unfortunately, it was too late for Jack.

"The repetitive continuous side effect of doing another breath-hold right after the laps is what led him to faint," she said.

"His body triggered a need to breathe and he sucked in a lungful of water. There was no oxygen going to his brain."

After 10 years, she said her message was getting through to some parents in the region who appreciated the family's efforts to highlight the dangers of hypoxic blackout. However, she said many were still unaware it could happen.

Mrs Washbourne said shallow water blackout is more likely to happen to capable and competitive swimmers rather than someone who can't swim.

"It doesn't happen to people to who can't swim because they are not the ones who go in and hold their breaths for long periods of time. It's the ones who like to challenge themselves and take risks."

Mrs Washbourne believes with children being more exposed to social media, certain things like breath-holding TikTok challenges can endanger them.

"And with the new Avatar movie out where Kate Winslet is said to have held her breath for seven minutes, how many kids is that going to affect?" she said.

"How many kids will get in the pool trying to be an avatar and trying to challenge themselves to hold their breath?"

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Mrs Washbourne emphasised the need for active parental supervision when it comes to water.

Together with her husband, Gary Washbourne, Mrs Washbourne started her business, Shallow Water Prevention Australia, to take Jack's legacy further.

"Jack died in his backyard pool the first summer they lived in that house and as hard as it has been for everyone, we've been focused to raise more awareness about it," she said.

This year Jack MacMillan would have turned 22.

"Michelle makes an annual visit to Illawarra Christian School to give out the sportsmanship award they created under Jack's name," Mrs Washbourne said.

Being a lover of all outdoorsy-things, Jack was known in the community for his interest in sports like cricket, soccer, tennis and swimming.

"His friends used to call him Harry Styles because he looked like him and he was just loved by everyone. They dearly miss him."