Looking at little Theo Jones, you would never know he was any different to most four-year-old boys.
But despite the big smile, the youngster is seriously ill and in desperate need of a heart transplant.
When a virus contracted shortly after he was born left his heart severely damaged, parents Willow Langdale-Smith and Colin Jones were told he would need the life-saving operation.
But Theo responded so well to initial treatment they began to hope he might get better.
However, his last routine test revealed a problem and he was put on the transplant waiting list a few weeks ago.
Willow and Colin, of Loughborough, have been told the average wait for a donor is about two years – so they are now facing a race against time.
"We were told when he was first ill he would need the transplant within a year, but he did so much better than they anticipated," said Willow.
"The last few years, he has coasted and each appointment they've said he was doing well. But at the last one, the doctor said something had changed and he didn't think there was anything else they could do.
"In terms of his heart failure, Theo is not as sick as some children, but the type he's got affects his lungs. And if his lungs are too damaged, he won't be able to have the transplant.
"We've been told it could be a prolonged wait – and some children die while on the waiting list.
"But then, I met a family who had been on the list two weeks and they got one. You never know.
"Really, this is it, now. We just want to get the call sooner rather than later.
"We've been told that when we get the call, there will be a car waiting for us within half-an-hour. We've already got a bag packed.
"But we've also been told we might have a few false alarms as well."
Theo caught the virus when he was a week old, and spent the first two years of his life on ventilation machines.
He takes several different types of medication and has also had a stem cell transplant as part of his treatment.
He is treated at Leicester Royal Infirmary, Glenfield Hospital and Great Ormond Street, in London, where he will be taken if a donor is found.
Willow has given up work to be his full-time carer.
"It's like having a newborn," she said. "He gets very ill – we've been back and forth to hospital three times in the last week.
"But he's also just like any other four-year-old boy – he loves Spiderman and pirates and Power Rangers. He's bright and bubbly and a happy boy but he doesn't have a lot of energy – he can't walk more than 100 metres.
"He's a very delicate child."
The couple have three other children – Sacha, 13, Tabitha, six, and Barney, two.
"I like to think we're a happy family but it does take its toll," said Willow. "I suppose we look like we're coping but underneath, it really hurts."
Willow wants to share Theo's story to raise awareness about organ donation.
"I'm all for the opt-out register, with everyone on the list unless they have reasons for not being a donor," she said. "There's such a shortage of organs."