Ali Gosper said the Supertee made her son Luca feel like he had "superpowers".

Miss Gosper recalled a recent appointment at John Hunter Hospital.

"He had his Supertee on - the one with the cape," said Miss Gosper, of Macquarie Hills.

"He was running through the hospital. I was like, 'you're so fast you're flying'.

"It distracts him from why he's there and puts him in a place where he's a superhero who can fight anything."

Miss Gosper said the Captain Marvel garment puts a smile on his face.

"When you know what he's going through, that's life-changing," she said.

Miss Gosper spoke to the Newcastle Herald to support Supertee's fundraiser Tea4Tees.

It asks people to host a high tea during April to help fund 16,000 Supertee care packs for sick children across Australia this year.

Supertee founder Jason Sotiris said it was a chance to "have some fun with family and friends while making a difference".

Mr Sotiris, a former tradie from Western Sydney, created the garments after his daughter Angela was diagnosed with a rare cancer.

"I knew nothing about medical garments, but I gave it a go," he said.

Luca was diagnosed with lymphatic malformation when he was one-month-old.

The rarity of his condition meant up to 20 medical staff at a time could be in a hospital room examining him.

The Supertee helped him with these stressful situations, as he didn't have to fully undress to see the staff.

The garments provide an easier way to treat children, as they have studs and velcro for easy access.

"I noticed in the last year that Luca is very conscious of his body," Miss Gosper said.

"When he has his three-month ultrasound, he has to get undressed and lay there in front of people he doesn't know.

"The Supertee gives him privacy, as it has buttons down the side. All I have to do is unbutton it on one side."

He can also wear the garment into surgery.

"It gives the doctors and nurses a talking point and makes him feel safe and comfortable before he goes in," she said.

Luca's condition caused soft spongy growths under and on top of his left arm and in his chest wall.

"It was the size of a tennis ball on his arm," Miss Gosper said.

The growths are non-malignant masses of fluid, believed to be caused by the abnormal development of the lymphatic system.

Doctors gave his parents two options to treat the growths - a chemotherapy drug or surgery called sclerotherapy.

They chose surgery.

His treatment has been at Westmead and John Hunter hospitals, with the surgery performed at the Sydney hospital.

"He's had two rounds of that so far," Miss Gosper said.

The first surgery drained the growths from his arm.

The second one treated growths in his chest wall, which were "too big and affecting his lungs and breathing".

"The results are amazing," she said, adding that he will face more surgery in future.

Visit fundraise.supertee.org.au.