This year's Sydney Morning Herald Half Marathon will be the 11th year Ms Smith's group, Running for Premature Babies, will don singlets bearing the names and handprints of her children, Henry, Jasper and Evan, and complete the 21-kilometre course to raise money for research and equipment to save the lives of other children born prematurely.

"Our triplets were born at 24 weeks, and we lost them to different complications common to premature babies," Ms Smith said.

"After the death of our final triplet Jasper at 58 days old, I was trying to come to terms with our unimaginable loss and Ash suggested I run the half marathon in their memory.

"Our aim was to raise $20,000 for one humidicrib for the Royal Hospital for Women."

Ms Smith was joined by 100 runners that first year, and ended up raising $80,000 for the hospital's intensive care unit, where her triplets were born.

The group, which grew to 520 runners last year, includes other parents who have lost babies or had children survive complications, and even runners who have themselves survived premature births.

"Last year, we had parents of five different sets of triplets on our team, four of whom had survived because of the life-saving equipment we provided," Ms Smith said.

"It's a healing experience to know that I've been able to turn a terrible tragedy into something so good and life giving."

The Coogee resident and former primary school teacher now dedicates all her time to Running for Premature Babies and is in the process of registering the running group as a charity in the hopes that it will continue to fund research and equipment for hospitals around Australia even after she retires from the project.

Ms Smith's husband died from brain cancer last year after an eight-year battle, during which he continued running the half marathon despite receiving chemotherapy and brain surgery.

Her eight-year-old son Owen is now planning to complete the course in a couple of years' time and maybe even take over the group one day.

"Owen has asked if he can take over Running for Premature Babies when I retire," Ms Smith said.

"He's doing the relay with me at this year's half marathon and running seven kilometres in memory of his dad and brothers.

"He says he wants to do 14 kilometres next year, and the whole thing as soon as he's old enough to register."

Anyone who joins the group is welcome to attend five weekly training sessions over 16 weeks ahead of the half marathon, and Ms Smith organises team barbecues, kids' discos and a race after-party.

"People who are at this stage struggling to run three or four kilometres and wouldn't have dreamt of running a half marathon, we're able to get them over the line injury free," Ms Smith said.

Runners can join the group when registering for the race, and are asked to raise a minimum of $200 for the cause.

• The Sydney Morning Half Marathon is on May 21, 2017. Early bird entries, where you can save $25 and earn 1000 Qantas points, are open until March 21. Register at smhhalfmarathon.com.au