"Parenting is scary enough in itself, but going through a heart transplant takes it to a different level," Dawn Birkland tells PEOPLE

Five years after learning that their newborns would need heart transplants, four mothers who connected at a Chicago hospital have formed lasting bonds, recently celebrating their childrens’ good health with a “heartiversary” party.

The Suburban Heart Mamas, as they call themselves, have been there for each other throughout their emotional journeys, sharing highs and lows as their kids have endured surgeries, setbacks and multiple hospital stays since their transplants in late 2011 and early 2012.

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Today, as their children run and laugh during playdates, the women brush away tears of joy, grateful for healthy outcomes after several years of stress and worry.

All four 5-year-olds are now flourishing, says Elfriede Pahl, medical director for the heart transplant team at Lurie Children’s Hospital, where the children had their surgeries.

“It’s so gratifying to see my four little patients running around together and thriving with their healthy transplanted hearts,” Pahl tells PEOPLE. “The families are taking such great care of them since they received the precious gift of life five years ago, and it’s a joy to see how well they are doing now.”

After experiencing the elation of birth, to suddenly learn that their newborns would need heart transplants was numbing and terrifying, says Dawn Birkland, 36, of Wheaton, Illinois.

Image zoom Dawn and Adelaide Birkland Courtesy Dawn Birkland

“Parenting is scary enough in itself, but going through a heart transplant takes it to a different level,” she tells PEOPLE. “Having a group of other mothers who get it is an immeasurable gift, and I will be forever grateful to them.”

Born with a severe congenital heart defect, Birkland’s daughter, Adelaide, had a heart transplant in October 2011, when she was just 1 month old. Birkland soon met three other mothers — Kaleigh Galliart, Stacy Hillenburg and Susan Zohner — going through the same trauma, and the women found comfort in each others’ kindness and advice.

Image zoom Kayleigh Galliart and Isla Courtesy Susan Zohner

“It’s so nice to have other women who have lived the same hell that you have, and share the concerns and fears that you do,” Zohner, 34, of Big Rock, Illinois, tells PEOPLE. “No one fully understands like these women do, and I’m so grateful to have gained them as friends.”

Zohner’s daughter, Piper, was born without a left ventricle in November 2011 and needed open-heart surgery at only a few days old, followed by a heart transplant a few months later.

“On the day Piper looked her worst and I had given up all hope of bringing my baby girl home, another family said goodbye to their child and gifted us with the ability to keep ours,” she says. “Every day, we celebrate the vibrant light that Piper is and all of the struggles she has overcome to be here with us. It’s been incredible along the way to meet other amazing moms going through the same struggles that we have.”

Image zoom Stacy Hillenburg and her son, Ben Courtesy Stacy

One of those women, Stacy Hillenburg, 40, of Bolingbrook, Illinois, helped put Zohner at ease during her daughter’s touch-and-go moments.

“A friend of a friend had asked me to talk to Susan, since we’d just been there with my son, Ben, who’d recently had his heart transplant,” Hillenburg tells PEOPLE. “We’ve ‘been close friends ever since.”

Ben received his new heart when he was 7 weeks old, after he was diagnosed with dilated cardiomyopathy, a disease more common in adults, where the heart dilates and doesn’t contract normally.

“When we learned he was suffering from congenital heart failure, everything in our world changed,” Hillenburg tells PEOPLE.

Having a group of women to talk to about her emotions “was a priceless thing,” she says. “Get-togethers between all of us aren’t as easy now as we’d like, but it’s hard to put into words how much these ladies mean to me. I’m able to ask them any question and know they won’t judge me or I’m think I’m crazy. I just know that they’ll always be there, no matter what.”

Image zoom Susan Zohner and Piper Courtesy Susan Zohner

After a normal and healthy pregnancy, Kayleigh Galliart, 30, of Bettendorf, Iowa, was shocked to get a call from her husband, Josh, informing her that their daughter, Isla, then 3 months old, was turning blue and that paramedics were on the way.

The Galliarts learned at the hospital that Isla had gone into cardiac arrest as the result of a rare heart condition and would need an internal defibrillator to regulate her heartbeat.

“We took her home for a couple of months, then when she was 7 months old, her little heart went out of control and her internal machine shocked her 75 times in one day,” Galliart tells PEOPLE. “That’s when we knew she needed a heart transplant.”

Image zoom Suburban Heart Mamas Courtesy Julianne Bardelle

Without her “heart mom tribe,” Galliart today wonders how she would have gotten through the traumatic ordeal.

“These women were a sounding board to make sure that I wasn’t overreacting or under-reacting to something involving Isla’s care,” she says, “and I knew that I could vent to them and they would understand. It’s been wonderful to celebrate so many milestones and victories together.”