William Reckless was diagnosed with the illness back in January, and spent three months in intensive care.
The youngster had to have his lower legs and part of his fingers amputated, and received a pair of prosthetics in May so that he could learn to walk again.
Now, after months regaining his strength, William has been getting used to his new way of life and getting around - with an emotional video showing the youngster walking on his own for the first time since he fell ill.
In the emotional footage, shot last month, William can be seen taking small steps towards his gran, Trish Brennan, who encourages her grandson to do 'a little bit more'.
Eventually William makes it to Trish and she gives him a kiss, while parents Gemma, 30, and Michael, 28, can be heard cheering with joy in the background.
Gemma, who lives in Nottingham, said: "When your baby takes their first steps it's magical but when they have to learn a second time, after months of watching their pain, fear, frustration, hard work and determination, the pride we feel is something else.
"It's been difficult for us to learn the world of prosthetic limbs, sockets, and liners, it's new to us all and we're learning as we go.
"He's been resilient for his age, the hardest part was at first when he was healing he preferred to crawl as he could get around easily like that and children don't see the endpoint when working hard towards something.
"But he now understands how important it is, we've turned it into a game for him and he's walking more and more now."
Gemma, who is also mum to two-year-old Georgia, said she took William to a GP when he started feeling unwell in January, and it was determined that he had a virus.
However, a worried Gemma sensed something more serious was at play, and took him to hospital a few days later - where he was induced into a coma within an hour of arriving, remaining in it for the next eight days.
Gemma continued: "Eight days is quite a long time for a child, other children were only on ventilators for a day and could then after a few hours chat with their parents.
"But William couldn't really interact with others for weeks, or say a word, and would stare straight through you, but then his speech came back so suddenly."
Young William was in the intensive care unit for three months, being treated for a blood clot in his thigh, a collapsed lung and a brain injury from lack of oxygen.
"It was awful when he first went into surgery and seeing him in a lot of pain," Gemma said.
"We were fortunate in not having any difficulties in accessing support, though (due to the Covid-19 lockdown) we've not had as many appointments as we would've done.
"Since leaving hospital he's had three physio sessions at the mobility centre, he's just got on with it, he's not moaned, and has accepted everything thrown at him.
"His sister didn't notice his legs and was just happy to have her brother home and her play-mate back after three months- she loves helping him to fetch things.
"He's still William. He's adapted amazingly well, he's still upbeat with a good attitude - better than most adults would."
Gemma shared updates on William's journey on the social media pages for her personalised gift business, Little Gems, which had to close when her son was ill.
The accounts have since turned into fan pages for William, who's become known as 'the conqueror'.
Now the Reckless family are sharing William's story further in a bid to raise awareness of sepsis, with Gemma adding: "So many people don't understand what sepsis is but the quicker you spot it the less damage and higher chance of surviving you have, for both children and adults.
"William had a lot of symptoms, a high temperature, a rash, not urinating. He was not just generally unwell, you know your child."
They are now also crowdfunding to help pay for William's future prosthetics, along with any adaptations to the home they need to make.
You can visit his JustGiving page here: www.justgiving.com/crowdfunding/letshelpwilliamwal...
Sepsis is a life-threatening illness, which iscaused by the body's response to an infection. Chemicals in the immune system release into the bloodstream to fight that infection, which in turn causes inflammation.
Symptoms to look out for include fever, blood clotting, less urination, breathlessness and unconsciousness.
Young children and seniors are also at a higher risk category than others.
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