Health Minister Mark Drakeford said £2m would be spent to cut waiting times for young people with autism and attention deficit hyperactivity disorder (ADHD).
He said the aim was to ensure "those with highest levels of clinical need are seen in a more timely manner".
An extra £600,000 will tackle diagnosis delays for all ages, improve training, and boost education and job prospects.
Meleri Thomas, from the National Autistic Society Cymru, said it had "long been campaigning with our supporters for the Welsh government and the NHS to address the distressing and unacceptable long waits for a diagnostic assessment in Wales".
"Some of our branch members report that they have had to wait an astonishing seven years for a diagnosis, which has a clear damaging knock-on effect in terms of ensuring that a child can access the right help early," she said.
"We will be looking carefully at the detail of these plans to ensure there is clarity for parents and individuals about how long they will now be expected to wait and to make sure they can access the right sort of help post diagnosis."
The spokeswoman said NAS Cymru was calling for an Autism Act for Wales to ensure children and adults across the country can get the support they need to reach their potential.
People with autism are being promised better diagnosis and support in a one-year action plan to improve services.