Now six years old, their parents know the boys - the only twins in the UK to both have the deadly Batten disease - may never reach the age of 12.
There is no known cure for the neurological disease and although both twins were born perfectly healthy, the degenerative disease will eventually shut down their bodies.
Both boys have now lost their sight and the ability to speak the few words that they had learnt, and they can no longer read their favourite childhood books.
Their mum Sarah Finney, 39, a trained nurse who lives in Nottingham with her partner Andrew Dawkins, 34, says: "It is heartbreaking watching the boys deteriorate and knowing that there is nothing that can be done. We are just making the most of each day that they are still here."
When Sarah fell pregnant with the twins, the couple were delighted. Andrew had been diagnosed with leukaemia at the age of 19 and doctors had told him they didn't know if he could ever be a father after having chemotherapy treatment.
"We didn't know if Andrew would be able to have children, so we were amazed when I fell pregnant," says Sarah. "When we found out at an early scan that I was carrying twins we were completely shocked.We looked at the scanning monitor and it was so emotional. They were like two tiny little beans moving around. It was amazing."
Both the twins were perfectly healthy when they were born, Freddie weighing 3Ib, 11oz and Louis weighing 4Ib, 2oz
"Louis had started saying 'mimi' for 'mummy' and imitating us saying 'one, two three,'" recalls Sarah. "Freddie was saying 'ta' when we handed him things. So even though they were slow to develop because of the autism, they were making progress."
But then just before the age of three, Sarah noticed that their eyes had started to flicker. And they started tripping over things:
"At first I thought that it was because the sun was in their eyes, or it was just that they were being clumsy. But when their eyes started to flicker, I knew that something was wrong. They would try and pick up objects from the floor and completely miss them. It was as if they were struggling to see."
The boys were referred to a paediatrician at the City Hospital in Nottingham. Tests discovered that they were both blind - despite having been born with perfect sight. Then in August 2010, they were diagnosed with Late Infantile Batten Disease.
"We were so shocked when we were told that they had lost their sight, as when they were born there had been nothing wrong with their vision," says Sarah.
"I'd heard of Batten Disease, and I knew it was something terrible. When the doctors told us that they both had it, it was devastating. I knew there was something wrong with them, but I never imagined it could be anything as serious as that. We were so shocked, we couldn't speak."
Late Infantile Batten Disease is an inherited disorder of the nervous system which emerges in early childhood. The condition leaves youngsters blind, bedridden, and mentally impaired and the life expectancy is between 8-12 years. There is no cure for it.
"It has been so hard to see both our sons born healthy, and then deteriorate like this. It is very difficult and frustrating for them as they don't understand why they can't see any more, or read their favourite books," says Sarah.
"It's hard because it's like having toddlers who can reach anything, so we have to be with them constantly. We took them on holiday to Portugal recently and they loved playing in the swimming pool. It was lovely to see them enjoying themselves. We have to take each day as it comes."
"It is difficult to think of a time when they won't be here. So we are making the most of having them with us."
A spokeswoman for the Batten Disease Family Association said: 'We are not aware of any other twins in the UK with this condition.'
Words by Lucy Laing
The family are supported by Genes for Jenes, a charity that helps children with genetic disorders. Their annual fundraising day is on October 5th.
Andrew is also fundraising for the Batten Disease Family Association.