The parents of a 3-year-old girl found out she had cancer after a cute photo of her falling asleep in a swing turned out to be a symptom of the deadly disease.

Dad Dave Fletcher, 39, thought he was capturing a tender childhood moment when he pictured daughter Izzy dozing off at a playground when she was 23 months old.

But just a few weeks later, Fletcher and wife Vicky, 37, from Worcester, England, were left devastated after their toddler daughter's tiredness turned out to be a sign that she had leukemia.

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The battling youngster has since undergone 570 doses of grueling chemotherapy and is now receiving maintenance therapy in a bid to stop the cancer from returning.

Fletcher said he thought nothing of it at first when he snapped Izzy nodding off in the swing at a park near their home in the city of Claines.

He is now warning other parents to be vigilant and look out for the telltale signs of the disease.

The couple first took Izzy to a doctor in January last year after a strange rash appeared on her leg. (SWNS)

"It was just an afternoon pop out to the swings. She was swinging away — I turned around and she had dropped off," Fletcher, an auditor, said. “She was drowsy and fell asleep but I didn’t think much of it. I thought it was a cute moment and just took a picture of her as you do."

"It was only afterward we realized it was all part of the symptoms and what I'd captured was her displaying signs of something more sinister," he said. "She had been tired, had had a few colds or viruses, and quite a bit of bruising on her legs. But we put all this down to normal childhood bumps and minor illness."

“You get a bit sentimental, looking at pictures of her before she was ill — you just realize how much she's been through since at so young," he said.

The couple first took Izzy to a doctor in January last year, after a strange rash appeared on her leg.

They were advised to come back several days later for blood tests if the rash had not gone away, and to take her straight to hospital if it got worse.

However, by the next morning, Izzy’s rash had spread and she then developed a temperature, so her parents took her to Worcester Royal Hospital.

She was diagnosed with leukemia the same day and began a course of chemotherapy the following week.

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Izzy spent her second birthday in Birmingham Children’s Hospital waiting to have a procedure to sample her bone marrow.

As part of her care, Izzy was enrolled on a clinical trial called UKALL 2011 and will remain on treatment until May of next year.

This trial aims to see if changing the standard chemotherapy treatment will reduce the side effects and help stop their disease from coming back.

"She has grown up very quickly and been subjected to medicine she doesn't like but has taken everything in stride so far," Fletcher said.

"When she was diagnosed, it came out of the blue. We were both in real shock as it happened so fast," he said. "It was a big unknown. A family member died of leukemia five years ago, so it was a scary time. We didn’t know what was going to happen at that stage or what the future held."

Brave Izzy has now received a Cancer Research UK Kids & Teens Star Award in recognition of what she has been through. (SWNS)

“But we were lucky Izzy was diagnosed quickly and lucky she has coped very well with the treatment, suffering very few setbacks or unplanned hospital admissions," he said. “The type of leukemia she has has a better chance of recovery than some others. She is young, which helps those odds."

“It makes us more optimistic. She doesn’t have to have so many steroids because of the trial she is on," Fletcher explained. "It’s a treatment plan they use in other countries and we are grateful to be given the opportunity. It shows just how important research is in pioneering new treatments. The NHS doctors and nurses have been brilliant, and we've had lots of support from family and friends."

Brave Izzy has now received a Cancer Research UK Kids & Teens Star Award in recognition of what she has been through.

“Izzy was so excited to receive her award. It was a nice positive experience that rewarded her for struggling on with her treatment," Vicky Fletcher, an archivist, said.

Jane Redman, spokesperson for Cancer Research UK Kids & Teens in Worcestershire, said: “Cancer can have a devastating impact on their lives and many of those who survive may live with serious long-term side effects from their treatment. Our mission is to fund research to find new, better and kinder treatments for young cancer patients."

“We want to bring forward the day when every child and young person survives cancer and does so with a good quality of life."