Heartbroken parents Lynsey and Duncan Brownnutt are treasuring every minute they have left with their beloved children.
Ellie Mae, five, and Caleb, three, may not live to see their teens after they were BOTH diagnosed with Late Infantile Batten Disease.
The condition is so rare that only five new cases are diagnosed every year in the UK.
The cruel disease, which starts at around the age of three, will see the siblings eventually lose their mobility, their speech and their eyesight.
And doctors have said it is very rare for children with the condition to survive into their teens.
The devoted parents, who were given the devastating news just one week before Christmas, are planning to make the most of their time with their treasured children.
They are looking forward to a family holiday in Disneyland, in America, this summer thanks to a generous collection raised by Duncan’s colleagues.
Lynsey 35, said: “Children with Battens can’t play or talk and they will lose all of that.
“It’s just like your worst nightmare and we just have to take it day by day.
“I can’t think too much into the future.”
Duncan added: “The best case scenario is that they will get to their mid-teens.
“The worst case, most horrible scenario is that we have got another five years with Ellie Mae.”
The family first realised there was something wrong when Ellie Mae started with epileptic seizures at the age of three.
Her development was delayed and just one month before her fifth birthday she completely lost her mobility.
Her little brother Caleb is full of energy and loves nothing better than playing football and running around.
But his parents fear it will just be a matter of time before he is confined to a wheelchair.
Lynsey from Cookridge, Leeds, said: “It will be really hard for Caleb when he loses his mobility.
“Ellie Mae has a buggy and a walking frame and I rely so much on the fact that Caleb can walk.
“I just don’t like thinking about it.”
Duncan, who is a store manager for Vodafone, added: “We have got pictures of Ellie Mae on her first day of school in her uniform and she walked to school that day.
“One month later she couldn’t walk at all.”
And the devoted father is currently enduring a 150 miles of pain challenge to help raise money for the Batten Disease Family Association.
The Association has become a support line for the family to help them cope with the devastating diagnosis.
Duncan, who is running five miles every day for a whole month, has already raised thousands of pounds for the charity.
He added: “Although this is a horrible situation and we’re still coming to terms with the news we have been overwhelmed by the support we’ve received.
“The Association, which is the only charity of its kind in the UK for Battens, have been a huge support to us and we are just overwhelmed.”