But while his parents were away for the weekend the little boy made a shocking discovery - he searched on the internet and found out his illness would progress and eventually cause his death.
Dominic Senior, 33, and wife Caroline, 42, returned home to find their son demanding to know why they had lied to him. Lil Dom has suffered from frightening nightmares ever since the shocking revelation
Mr Stacey, a youth worker, said: "We've always drip-fed him information about the condition which he calls his 'tired legs'.
"He understands the effects of the condition but it's very hard to explain to someone so young. He has asked us in the past if it would kill him and we've always told him that no one knows when they're going to die."
The father, from Holsworthy, Devon, said the aftermath of the discovery has been heartbreaking for the whole family.
He said: "He came up to me and asked me why I had lied to him.
He had looked up the disorder online and found out that it will eventually kill him. We sat him down and explained everything. It was one of the hardest conversations I've ever had. We were all in bits.
"Since then he's had several nightmares about it and always calls us in for a cuddle.
"He just wants to know we're here for him. One night he asked me to find a cure for his condition and that hit me like a sledgehammer. I wanted to say yes, but it was so hard."
Dominic said his son very rarely talks about his condition now and has received a lot of help from his palliative care nurse.
Lil Dom said he still leads the normal life of an eight-year-old. He said: "I like history and maths at school and at home I enjoy drawing and playing on my Xbox. I like playing with my friends but I can't do it for too long because my legs start to hurt.
"Luckily my school let me have a sleep in the afternoons if I'm tired. I also have to eat a lot to keep my strength up. I'm an eating machine. The other day I had a whole seafood platter all to myself."
Dominic and Caroline, a psychiatric nurse, have three other children: Cate, six, Georgia, four and two-year-old Tahlia.
Around 2,500 people in the UK suffer from Duchenne, which is most common among boys.
Lil Dom also suffers from a form of epilepsy known as absent seizures, which means he can have up to 20 memory blanks in one day.
For the past four years his father Dominic has organised fundraising events in aid of Duchenne, including swimming with sharks and a mass Chinese lantern release.
His proud son said: "He's done some crazy things like dress up as BA Baracus and wear a silly mankini, I thought both of those were really funny.
"I like being at the events. I was sat on top of my friend's car to see all the lanterns released last year, it was great.
"I was amazed so many people turned up, it was really nice that they supported the charity."
The family have also thrown their support behind a song called 'Nobody Knows Their Time,' which has been written by Dominic's friend, Mark Emmins.
The song is released on digital download on March 4 and is available on iTunes for 99p, with 40p from each sale going to the charity Duchenne Now.
What is Duchenne's muscular dystrophy?
It is an inherited disorder that causes progressive muscle weakness.
It usually only affects boys (around one in 3,500), although girls can carry the defective gene.
It is not apparent at birth but symptoms appear in early childhood.
Boys with Duchenne will have difficulty with walking, jumping and climbing stairs.
The condition is diagnosed via a blood test and muscle tissue sample.
Most people with Duchenne survive well into their 20s and sometimes longer. The eventual cause of death is usually a severe chest infection at the stage when lung function is already poor.
You can find out more about Duchenne at www.duchennenow.org.