Image copyright Hayley Grix

On 17 April, weeks into the UK's coronavirus lockdown, three-year-old Marley Grix was admitted to hospital.

He'd been ill for a few days - since Easter Monday - but his condition had taken a turn for the worse.

Marley's mum, Hayley, feared his life was in danger and knew she had to act quickly.

"He'd started off complaining about his neck saying it hurt, but it didn't seem bad and I just thought that perhaps he had slept funny.

"But for the rest of the week, he just kept getting progressively worse. He had diarrhoea and stomach pain and a temperature. I was on the phone to the GP pretty much every day. Phoning, videoing."

On the Friday, Marley was very ill, and he had symptoms that were scaring Hayley.

"He was really tired and he had a roaring, high temperature that wouldn't go down. His neck glands were swollen.

Image copyright Hayley Grix

"His hands and feet were bright red and his eyes were bloodshot. And he was breathing really fast. It was terrifying.

"I called the GP again, but decided to take him to hospital. I followed my gut instinct."

The doctors in the paediatric unit admitted Marley and started running tests to figure out what might be wrong.

They suspected a few possible causes, including a bad reaction to coronavirus.

Doctors around the UK have been warning about a rare but serious syndrome that could be linked to the pandemic virus.

Some of these very ill children have had a septic-shock type illness with a rash and difficulty breathing.

Health Secretary Matt Hancock has said that he is very worried about it and that experts are looking into this rare condition.

Marley's coronavirus test came back negative and his doctors are now treating him for atypical Kawasaki disease.

This is another rare condition that mainly affects children under the age of five. Children who develop it may be genetically predisposed to doing so.

The symptoms are like those seen when the body is trying hard to fight off an infection. And it is one of the conditions that mimics the new mystery illness which doctors think might be linked to coronavirus.

Symptoms include swollen lymph nodes, fever and in severe cases, inflammation of arteries of the heart.

Marley has been discharged from hospital but Hayley hopes sharing her story will help other parents who may face a similar dilemma to her own.

"All I can do is share this message. Seek help immediately if your child is unwell and your gut is telling you something isn't right. You know your child.

"I know people are reluctant to go to hospital because of coronavirus. You might think you are doing them a favour by keeping them at home but if they are really ill then you have got to seek help."