Young people with learning disabilities have been “marginalised and often hidden from view”, according to the Children’s Commissioner for Wales.
Prof Sally Holland said they were not getting the support they were entitled to by law.
Lucy Williams, from Wrexham, has Asperger’s and said for years she thought “there was something quite weird about me”.
The Welsh Government said it had announced it was improving services.
The Welsh Local Government Association (WLGA), which represents councils, has been asked to comment.
Prof Holland’s report looked at the experiences of young people with learning disabilities as they become adults.
It found that despite legislation, young people and their families found it difficult to access support and were often left with little or no information about where to go for help.
Laws to help young people
Under the Social Services and Well-Being Act, young people who need care and support should be involved in designing the care they receive and should have easy access to the right help and information.
And services such as health and education should also work together to give people care that meets their needs.
Meanwhile, the Well-being of Future Generations (Wales) Act states that the services they receive should also be flexible.
A total of 83% of the 187 parents surveyed said they were worried their children were socially isolated and many highlighted concerns about bullying.
Prof Holland said: “This can be such a fearful stage for young people and their families.
“It needs to be much smoother, much more well-planned, and services need to work together to make sure that the care offered to each individual family meets their needs.
“We already have some key legislation in place. The next step is to improve how it is delivered.”
“For years I knew there was something different about me,” said 17-year-old Lucy Williams, from Wrexham.
She has Asperger’s Syndrome which is a form of autism.
“I think things differently, I see things differently,” she said.
“I thought there was something quite weird about me and then my mum told me I have this additional need.
“I’ve got used to it now and it feels pretty good. I feel a bit different but it’s something I live with.”
Read more at: https://www.bbc.com/news/uk-wales-44741905