When proud mum Mari Barnes arrives on the school playground each afternoon, she sees her happy and active son Stanley with his friends.
But instead of running over to her, she faces the heartbreaking reality that he doesn't recognise her and can't pick her face out of the crowd of other parents.
Little Stanley, who is just eight years old, lives with Sanfilipo, a condition likened to Alzheimer's in how it affects the brain.
He was first diagnosed with the cruel condition when he was just 16 months old, to the devastation of 40-year-old Mari and her husband Ross, 44.
As his condition has deteriorated, Stanley has lost the ability to communicate with his parents, forgetting simple words like "apple."
Mari, from Falmouth in Cornwall, said: "He's quite dramatically gone downhill this year - he's lost all his words.
"It's really hard, it feels like you're losing part of him each day. This is rapid, just six months ago he might have been able to acknowledge you or say something."
Although Stanley's condition is complex, Mari describes it as like "childhood Alzheimer's" which causes him to lose skills as his cognitive ability declines.
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She said: "The minute I leave the house I have to hold his hand, otherwise he just goes off in a different direction."
Devastated Mari added: "Over the weekend he had a burger, and managed to say the word burger, and honestly I nearly cried. We haven't had that recognition or anything for quite some time.
"It makes it all the more special to know that he is still in there."
The horrible illness means Stanley's life expectancy is between 10 and 20 years old - and the family plans to make the most of every day of his life with his siblings Willow, 11 and Orson, six.
In terms of his cognitive ability, Mari said Stanley is currently operating at the level of an eight-month-old.
Desperate for a cure, Mari and Ross enrolled Stanley in a medical trial at Great Ormond Street Hospital when he was just two.
She described: "It was really quite invasive, they put a gate inside his body that went into his spinal column.
"They then injected that port with the enzyme that he was missing every two weeks, so that was quite full on.
"We were on that trial for two years which kind of gave us a bit of hope that it would slow down the progression of his disease a bit and give him a better quality of life for longer."
The mum reckons the trial did help Stanley a little, as he seems to be in better shape than other kids his age with Sanfilipo.
However, the family is taking each day as it comes, making sure Stanley enjoys everything he does.
"We are just trying to give him as many joyful experiences as possible," Mari said. "I'm no longer trying to teach him new skills but we are trying to maintain ones he has already learned."
One such skill was encouraging little Stanley to walk 10 miles over the space of a week last year to raise money for Children in Need - raising an incredible £5,000 and even appearing on the show.
Mari now wants to share her experience of parenting a child with Sanfilipo so others in her position feel less alone.
She said: "His first year was relatively normal. Then I saw a big change in him after that. He just stopped hitting those milestones, and we got referred to a paediatrician - so we got a really really early diagnosis.
"A lot of children don't get diagnosed until school age, people tend to just think the child might be autistic, but then it's bizarre because they'll have the word for 'apple' one day and then not have that word the next day. Or they might have forgotten how to do a task like pick a pen up, things like that - so those are the alarm bells around it all.
"They have shorter limbs, and larger eyebrows, and a blackened nose bridge - it looks quite sweet in a way - but it can get stronger as they get older. It's just a result of the disease."
Explaining how the condition affects the brain, she said: "His cells are lacking in enzymes that clean out toxins, so as he gets older those toxins get built up - and so everything starts to shut down."
While Stanley is still physically able to do most things, Mari has noticed he's "stiffening up" and isn't walking as far as he once could.
The parents have kept him in mainstream school for the time being and hope he can stay there as long as possible.
"Unfortunately with teaching him language, he has lost that skill now," Mari said. "There's nothing more we can really do, so you have those kinds of daily 'bad news' phone calls from professionals.
"We know he's losing skills, but then the fact he can still walk ten miles and raise five grand for charity shows he still has such an effect on people. He's so positive."
Recalling the day she found out about his diagnosis, Mari said it was "horrific" - but she was determined not to waste any time with him.
She said: "It wasn't this little boy that we had in front of us. It certainly wasn't our story yet."
Although Stanley has declined rapidly during the last six months, Mari says there are glimmers of him that shine when he remembers something.
She explained: "Like with Alzheimer's, he has some early memories he recognises. Like if we walk past the nursery for example he sometimes tries to go in, and he remembers songs we used to sing to him because his face lights up.
"He loved Frozen for example, so if that ever comes on the TV he gets so excited and might stand up and jump and yell around the TV."
But nothing is certain for the family and Mari admits: "I don't know how much longer that will last."
Do you have a story to share? Email jessica.taylor@reachplc.com.
