As three-year-old Eamon Obst puts on his favourite superhero cloak to fight cancer, a village of online supporters is rallying behind him by donating money.

In one week, $23,000 has been raised through a crowdfunding appeal on the GoFundMe website.

For Adelaide parents Justin and Kathy Obst, the donations will ease the financial pressure to return to work as they juggle Eamon's hospital treatment with caring for his 12-week-old baby sister Isla.

Family friend and campaign organiser Michael Arnold, of Loxton in South Australia, said the response had been overwhelming.

"It was unreal. I think people put themselves in Justin and Kathy's situation," he said.

"A lot of our friends [in their 30s] have got kids and just can't believe how hard [this is] and what sort of battle they've got."

Eamon had a special visitor at the Women's and Children's Hospital in Adelaide. ( Facebook: Eamon's Kicking Cancer's Butt )

Cancer diagnosis after unusual coloured urine

Eamon was diagnosed with Wilms Tumour, a cancer of the kidney primarily found in children, after his parents noticed his urine was an unusual colour during the Easter weekend.

"That small thing has led to the diagnosis, and now he is in the best hands at the Women's and Children's Hospital," Mr Arnold said.

"Before that they had two happy, healthy little kids leading into Easter.

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"They just noticed one small thing and now their world has been flipped upside down. They have a battle on their hands that's for sure."

Superhero inspiration

The boy who loves to dress up as his favourite superhero, Batman, has inspired a bedside visit from the caped crusader, as well as a quick trip to the shops to make his hospital stays more comfortable.

"Friday morning we went and bought our boy some comfy clothes for hospital, including a very cool Batman hoodie and Batman slippers … he's all set to kick cancer's butt Batman-style," Ms Obst wrote on Eamon's Facebook page.

Mr Obst said his son had always loved Batman.

"The idea of Batman as his mascot evolved and is quite fitting," he said.

"The thought that an everyday person with no superpowers can become a hero to so many. It's like Batman gives him powers to fight this thing.

"That's how we as a family think of Eamon — a brave little hero with immense power to fight."

Eamon's Kicking Cancer's Butt campaign has been shared on social media more than 1,000 times, and donations have poured in from more than 200 people.

It has gathered momentum in Adelaide and also the Riverland community, because Mr Obst grew up in Loxton.

Ms Obst wrote a message on the campaign webpage to thank supporters for their messages and donations.

"Humbled beyond words. Thank you all for your kind donations. It's amazing how our world is so small and so kind when you really need it," she wrote.

Personal crowdfunding campaigns on the rise

Crowdfunding websites started appearing about a decade ago, but in the past five years they have broadened from kick-starting business ventures to fundraising for personal causes and charities.

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Social researcher Mark McCrindle said studies showed Australians were most passionate about children and medical causes, and were more likely to give if a cause was local.

People also preferred to give on a once-off basis without being solicited for ongoing donations.

"When you've got a situation like this that involves a child, and it's medical and it's local, that's where Australians are prompted to help," Mr McCrindle said.

"These causes that come across our social media feeds, they hit us at the heart and we say 'There's someone in a fair-dinkum situation' … and by clicking here, one-click giving as it's called, I can make a difference'.

"That very much suits the style of giving and the big heart of Australians, particularly when combined with technology in this era."

Eamon Obst playing with dad Justin at the Women's and Children's Hospital in Adelaide. ( Facebook: Eamon's Kicking Cancer's Butt )

Complications force specialists to reconsider treatment

Eamon was back at the Women's and Children's Hospital on Monday after complications from the tumour, and specialists were reconsidering the best approach to remove the cancer.

Treatment options being considered include surgery, chemotherapy and radiation therapy.

Mr Arnold said despite the strain on the family, Eamon was coping admirably.

"He's a trooper, he's a happy smiley little guy," he said.

"He's got drips, needles, catheters and all sorts of things going on and you could imagine how that would go for a little three-year-old, but every time I ask Justin how he's going he says 'Surprisingly good'.

"He just keeps smiling and pushing on."

And Ms Obst has an important message for other parents.