"We were so grateful his cancer was gone, we felt it was important to give back," says Holt-Witt.
So Gretchen and Liam, a joyful risk-taker of a kid who loved to cook – "he'd download tons of cooking apps," Holt-Witt says – decided to pay it forward. They came up with the idea to bake cookies to raise money for pediatric cancer research. But a few dozen wouldn't do. They opted for 8,000 dozen.
"We wanted to push our boundaries the way Liam's had been pushed," says Holt-Witt, who along with her husband Larry, daughter Ella, and 250 friends and volunteers churned out 96,000 cookies, raising more than $400,000.
Holt-Witt founded the non-profit organization Cookies For Kids' Cancer. People all around the country hold bake sales in the name of the organization to take up donations for pediatric cancer research.
Now celebrating its fifth year, CFKC has raised more than $5 million for research and development of new cancer treatments for kids and this year published a new cookies cookbook, with proceeds going back to the charity.
"There aren't that many treatment options for kids because pediatric cancers get the short end of the funding stick," says Holt-Witt. "Helping others is what allows me to cope."
Shortly after their bake sale, Liam's cancer returned.
"He went through tons of relapses," says Holt-Witt, "It was kind of like building a house in the sand, the foundation could give away any second."
But despite constant trips to the doctors office, and countless rounds of chemo and radiation, Holt-Witt says "Liam didn't know he was sick. I'd say, 'Oh we're just going to spend a few more days at the hospital, no problem.' Seeing me worry was not going to make life easier for him."
First diagnosed as a toddler, Liam never showed any telltale signs of the illness. For four years Liam underwent countless clinical trials. Despite the treatment and doctors' best efforts, he never reached his seventh birthday.
"Missing her brother and losing her only sibling will never go away," says Holt-Witt of her daughter Ella, 7, who often comments on things Liam would have liked to do and see. "But Cookies is an outlet for her, because she feels like her bothers life had meaning and wasn't in vain."
The organization has now helped fund their seventh clinical trial project, meaning new hope for young cancer patients around the world.
"Cookies gives anybody, anywhere something tangible to do to help with such a daunting issue. It makes you feel like a hero," says Holt-Witt. "I know this sounds strange, but I feel like one of the luckiest people out there because I get to see the good in people. To have the opportunity to receive access to a new treatment is the equivalent of having a chance at bat."
That's a chance Morgan Pierce has now. The 10-year-old from Plant City, Fla. is currently receiving lifesaving cancer treatment through a new clinical trial that Cookies help fund.
"That's what keeps you going," says Holt-Witt. "I don't have my son here to hug and hold and love, but I'd still do anything for him. I know the first thing he'll say when I see him in heaven is, 'Mommy, did you make it better for others?' And my husband and I will have to look at him and say 'We did everything we could.' "
Know a hero? Send suggestions to firstname.lastname@example.org. For more inspiring stories, read the latest issue of PEOPLE magazine