For most families a birthday is usually a cause for celebration.

But for parents Cat and Chris Sweet it's a reminder of how cruel life can be.

Because every birthday marks a year their three children get one step closer to permanently needing wheelchairs due to their rare conditions.

"I'm really strong most of the time but I always have a wobble on their birthdays," Cat says.

"I hate it because it's one step nearer to a bad day."

All three of their children, Louisa, 16, Max, 13, and Harry, seven, have life-limiting illnesses which will get worse over time.

Harry has suffered with Ehlers Danlos syndrome since birth, which causes him so much pain in his joints that he struggles to sleep and in 2017, genetic testing found that Louisa and Max had Friedreich's ataxia, a rare and neurodegenerative condition.

An army of volunteers gathered to lend a hand

Cat, a full time carer for the kids, says: "As each year passes, in that 12 month block there's always something that's been a deterioration.

"Even since these last birthdays, Lou's walking is much worse, Max has developed the arrhythmia - a dangerous rhythm in the heart. Each birthday is another closer to a time when they won't be able to manage so well."

To make matters worse, their home in Weston super Mare is too small and inaccessible for children who will someday soon become full-time wheelchair users.

"In six months time I've got three full-time wheelchair users in my house and my house is like this," the 35-year-old says.

"I don't know how that's going to work. I can't physically move my children any more.

The show transformed the home, and has made it more wheelchair-friendly

"I'm scared that will happen before we've had the chance to do anything. We won't have anywhere to live anymore."

Those fears have been alleviated by DIY SOS and an army of selfless volunteers who stepped in to help transform the home into an accessible haven.

Before the build Cat was having to lift her children in and out of the bath and carry them up the stairs.

Now the family have a wheelchair-friendly bathroom with hoists which will let the kids be independent.

The team also installed a lift so the children don't have to use the stairs and inserted hoists in each of their bedrooms to help them get in and out of bed for when that time comes.

The team installed a lift for the children

The refurbishment been even more of a lifesaver this year because all three children have been shielding from coronavirus, meaning they have been home-schooled for the entire year and haven't been able to see friends.

Cat says without DIY SOS's intervention they simply wouldn't have coped.

"We were suffocating in that house," she says, "but they fixed something for my children that I couldn't fix myself."

It wasn't until Louisa hit her teens in 2017 Chris and Cat realised something wasn't quite right.

As a child everything was normal except for one thing.

Chris, 42, says: "We'd always noticed when she was younger she seemed a bit clumsy - just a bit of a klutz. When the professionals looked at her they saw more than what we had.

"Then before her 13th birthday, everything normal stopped. The consultant said they were concerned about her because she wasn't walking in an age appropriate manner and her balance was quite poor."

Nick Knowles fronts the programme

They diagnosed her with Friedreich's ataxia and soon after, the parents were delivered a second blow that son Max had it too.

Now the condition with his heart means he is in more immediate danger than Louisa.

"It feels like Max is a ticking timebomb," Cat says.

"This condition is killing them. There's nothing I can do, no operation, no pills, the trial studies have fallen through. One day I'm going to wake up and one of them isn't going to be here anymore, how do you compartmentalise that?"

And heartbreakingly, Cat reveals to Nick Knowles how her daughter once said she doesn't have any dreams and doesn't look to the future.

"I had a conversation with Louisa and asked her if she had any dreams about travelling, a job… and she said, 'I just don't have any'.

"And that's really sad. As children they don't have dreams of anything anymore."

But after the transformation on their home is complete, it made the family realise how loved they were by the community and gave the children something to hope for.

There was a lot of work to be done

Cat says: "There are still huge challenges they face, we're in a real transitional period where things are deteriorating rapidly, and her fear is she will lose her motor skills and not be able to draw anymore.

"Now she says things to me like, 'Will I be able to push my baby's pram?' She's thought that far in front, she wants a family.

"Max wants to go to university, Harry wants to be a policeman, Lou wants to work with animals. They all want to do things. I cannot explain to you how much this has changed our lives."

Cat and Chris shared their kids' hopes and dreams

The future is uncertain - life expectancy with Friedreich's varies significantly depending on the severity of the symptoms - but Cat and Chris try not to dwell on the very harsh reality that they could outlive their children.

Crucially though, they've been given a space where they can enjoy being a family which also serves as a reminder of the kindness and love from their local community.

"The house isn't the big thing, it's not just bricks and motor," Cat says.

"When you give a family like ours a home, it's not just the security and a long-term environment. They've given us hope and given the children back their dreams."

*DIY SOS: The Big Build is on tomorrow night BBC One, 8pm and on iPlayer.