"Yuta was breech (in a bottom-first, not head-first position)," Kyoko says. "The doctors tried to turn him around so I didn't need a caesarean, and discovered the growth."
Kyoko couldn't believe the diagnosis, "I was like … whaaat? My son has what?! The ultrasound looked perfect, and I couldn't believe he could be sick."
To avoid a complicated natural delivery, Kyoko underwent a caesarean section and baby Yuta was delivered on Christmas Eve, 2011.
"I was allowed to give him a kiss, and pose for a photo, before he was whisked away by the doctors and nurses," she says. "It felt surreal, as it was very different from the birth of my first baby two years earlier."
On Christmas Day, while most of us were busy unwrapping presents and over-eating, little Yuta underwent complex surgery to remove the huge growth.
"I found out many months later that Yuta's cyst was the biggest the doctors had seen in a decade: it was the size of a grapefruit," Kyoko says.
"He had 14 centimetres of his intestine removed, and a hole in his stomach repaired where the cyst had been."
The surgery was a success, but there would be a slow road of repair and rehabilitation ahead for Kyoko's newborn baby.
Yuta spent the next three months in The Sydney Children's Hospital, where his parents and sister, Emi, dutifully visited every day.
"Looking at my son, all covered in tubes, I felt devastated that there was nothing I could provide for him," Kyoko says. "All I wanted to do was to help him get better."
"The only thing I could do was express my breast milk for him – so several times a day, every day I would pump it for him, just to make myself feel like a mother."
When admired for her persistence, Kyoko smiles, proudly explaining, "I finally got to nurse him myself when he was four months old, and he fed until he was one-and-a-half."
It was a long hospital stay for baby Yuta and his family, but Kyoko says she was extremely well supported by the staff and the other families being treated at The Sydney Children's Hospital.
"It was like having another family, to be honest. I obviously enjoyed seeing my son everyday – and marking his progress – but I was always keen to see the other children and their parents, too."
For Kyoko and her husband this support was vital, as their extended family live in their native country Japan.
"I never worried about my parents being far away until my son got sick," Kyoko says. "Suddenly I realised how important it is to have family nearby."
"The hospital became our second home, we felt nurtured, and I felt safe leaving my son with them."
After a myriad of blood tests, scans and check-ups with paediatricians and other specialists, baby Yuta finally went home in March 2012.
"We felt so blessed and so thankful to finally take him home," Kyoko says. "I was worried about losing the support of the hospital, but they have continued to be there for us."
Two and a half years on, and Yuta is your typical toddler.
"He is very determined, and his favourite word is 'no'," Kyoko says. "You wouldn't know that he had been through anything, he has enormous energy and is always running us off our feet.
"We just feel lucky he was diagnosed so quickly, and looked after so well."
Help light up the lives of sick children this Christmas by buying a Little Light to raise funds for The Sydney Children's Hospital to provide vital equipment and support for kids like Yuta. Visit the Little Lights website to purchase a light on the virtual Christmas tree for yourself or the perfect gift for a loved one.