Being born with a rare genetic disorder may sound unlucky. In fact, there are so many different types that more than one in every 25 children born in the UK has a genetic disorder – that's 30,000 children a year. It means that the health problems associated with genetic disorders are the biggest cause of death of children age 14 and under.

"Some genetic disorders are apparent at birth, whilst others are diagnosed at different stages throughout childhood, and sometimes even in adulthood," explains Caroline Harding, CEO of charity Genetic Disorders UK. "The majority are extremely rare – some don't even have a name yet – which makes diagnosis extremely difficult. Families often struggle to get the correct diagnosis, care and support for their child. Other challenges include finding the right school, telling the rest of the family and finding other families living with similar conditions."

Abbi Thompson's son, Ethan, is two. When he was born, Thompson noticed dark patches on his face and body. He was whisked away for checks but nobody knew what they were. "When we got home from the hospital I started Googling, desperate to work out what the problem was. Not knowing was frustrating. And so was the fact that we had this gorgeous newborn baby, but we couldn't just enjoy him, because everyone was asking what was wrong. And all we could say was: 'We don't know.'"

Finally, at three months, Ethan was diagnosed with Congenital Melanocytic Naevus (CMN), which causes large moles – some of which are puffy and covered in hair – to form over the body. It can also impact on the brain and nervous system, but an MRI scan at 12 months showed only Ethan's skin was affected.

"Once we had a diagnosis, it helped. Then we were invited to a family day by the CMN charity, Caring Matters Now. I was nervous, but meeting other parents has made such a difference, and seeing the CMN kids play together brought a lump to my throat. There are only a few hundred CMN children in the UK, so you're not going to run into someone at your local playgroup."

Thompson finds it hard when people stare at Ethan – she'd rather people just asked what was wrong. "But, as isolating as it can be, it's important for Ethan to have as normal an upbringing as possible. And I want to have all the normal mum conversations about fussy eating and potty training. I have all these worries too."

"Sometimes I think, this is unfair. It's hard to keep that up though – Ethan is an outgoing boy and, in a way, he wouldn't be Ethan without CMN. But the challenge will be when he gets to school. Our society is all about looks, and I just hope he's got the confidence to deal with bullies. For now, all we can do is give him the best start in life we can."

For Anna Eaton, whose sons Archie, 13, and Isaac, 11, both have Morquio Syndrome, a diagnosis came later. Archie was a normal baby until he developed a few hearing problems. "It was put down to glue ear. He was also slow at speaking, and then I noticed his chest shape seemed strange."

Morquio Syndrome affects bone development and restricts growth, but it is so rare that it wasn't until after Archie's brother Isaac was born that he was diagnosed. Then Anna and her husband, Dave – who both just happened to have the recessive gene – had to play a waiting game, wondering if Isaac was affected too.

"It was around the time I was taking the boys to baby and toddler groups. I was trying to process Archie's diagnosis and wondering if Isaac had it, too. I'd be listening to all the mums moaning about how little sleep they'd had the night before. Half of me felt that of course they had a right to complain. But half of me wanted to shout, 'You have no idea how lucky you are …'"

"The boys' diagnoses had big implications for the future, but at the same time, nothing changed. When you have a baby and a toddler, you just have to get on with it. Now, they both use wheelchairs but they're at mainstream school and they're getting on fine.

"I used to feel self-conscious on their behalf but I don't any more. If I could go back to that baby group, I would say to the me of 10 years ago, 'Take it one day at a time. Life will be normal again – just not the normal you had in mind.'"

Charlie Howram is eight and his entire family has joint hypermobility, which has been diagnosed in Charlie as a variant of Ehlers Danlos Syndrome (EDS), which adversely affects collagen in the body. He suffers from regular joint dislocations, extreme pain and fatigue.

Charlie's mother, Melanie, remembers the day that she and her husband Mark got a diagnosis, after months of pushing for more tests. "We had to grieve, just to be able to carry on. When you get pregnant, you dream a future for your child, and when it's taken away, you need to deal with that."

Through the Hypermobility Syndromes Association, Howram and her family have learnt to manage Charlie's symptoms. "It's hard though. Sometimes he asks why he can't be normal. My heart breaks but I can't let him see that. 'What do you want to be normal for?' I ask him. 'Normal is boring.'

Howram finds she gets a few negative reactions, mainly because EDS is often an 'invisible illness'. "Charlie doesn't always need his wheelchair, sometimes he gets out – you should see the looks we get. A sense of humour gets you through. And I still think we're lucky. We have to feel lucky – if we stop thinking that, what do we have?"

• Jeans for Genes day on 19 September raises money for Genetic Disorders UK. Further info: Jeansforgenesday.org