A community of women have pitched in to help babysit the children of a Sydney woman so that she can participate in fundraising marathons, after she lost her husband to brain cancer.

Several members of the Coogee Cougars women's running group made the offer to help fellow member and mother-of-two Sophie Smith after her husband’s death earlier this year.

Ms Smith, 46, regularly runs with the group and was about to give up her regular 5.20am run after realising she had no one to help mind her two young sons Owen and Harvey.

Coogee Cougars founder Jo Davison, 47, then asked her fellow runners if they would be willing to give up their run to help mind the two boys.

Ms Davison said the response was "instantaneous".

"People were willing to just go ‘yes’, to give up both their time at an early hour of the morning as well as the chance to run (to help babysit)," she told 9news.com.au.

"They were giving of themselves — that’s what made it so special.

"There’s a bigger unity that binds our group together than just the running itself — a connectedness between Sophie and people in the community who care about her and want her to still be able to share."

Thanks to the intervention, Ms Smith now has a rotating roster of "Cougar Ladies" on call to help with morning child-minding so she can continue running.

Ms Smith has called their offer "the kindest, most thoughtful thing anyone has ever done for me".

"I have felt incredibly supported through my loss by (the "Cougars") and have come to know so many more women in the group as a result," Ms Smith told 9news.com.au.

Since the offer, Ms Smith trained and ran in last month's New York City Marathon, running in a group of 17 and raising a total of $185,000 for the Royal Hospital for Women in Randwick.

She is now organising a team of 500 to run in the 2017 SMH Half Marathon in May, during which she hopes to raise at least $100,000.

Ms Smith also happens to be the founder of charity Running for Premature Babies, which has raised more than $1.5 million in support of Royal Hospital for Women’s Neonatal Intensive Care Unit (NICU), benefiting more than 1800 babies since 2007.

Coogee Cougars founder Jo Davidson and her group. (Jo Davidson)