Families of children with autism say they have been short changed under the National Disability Insurance Scheme, with early intervention therapy provisions falling far below international best practice.

Participants in launch sites have been told they will received funding for less than six hours of therapy a week, less than a third of the recommended 20 hours.

Monika Dobek has been spending about $35,000 a year on 20 hours a week of evidence-based applied behaviour analysis therapy for her six-year-old daughter, Olivia, who was diagnosed with autism two years ago.

She was delighted when she was told Olivia would be eligible for funding under the NDIS in April but stunned to discover the money would only cover six hours of therapy a week.

"I had really high expectations from the NDIS and I thought it would be a fantastic thing for us but I have been quite disappointed to find that it’s more about money than the individual's requirements," she said.

"I told the NDIS planner about the therapy we had been doing and the costs involved and she said $14,000 would be adequate. That will only cover six hours a week.

"We want to give our daughter the best chance at life. If we are only giving her six hours, we're giving her less than half a chance. I am quite astounded."

Ms Dobek’s experience is not an isolated case, according to Nicole Rogerson, chief executive of Autism Awareness Australia. Families have told her their NDIS funding for early intervention is being "capped" at about $16,000 a year.

"The internationally recognised best practice guidelines are 20 hours a week of early intervention – $16,000 is just not going to cut it," she said.

"If the government wants to cap the funding at $16,000, that's a budget decision. That's not in the best interests of the child."

Ms Rogerson said the scheme would ultimately waste money as children would not fully benefit from less or lower cost therapy.

"If somebody is prescribed 10 tablets for their problem, you don’t give them two tablets and say that will cure it," she said.

A spokesman for the NDIS denied that funding was being capped, saying it would cover "reasonable and necessary" supports at a predetermined price benchmark.

"A benchmark price provides an estimate for planning purposes," he said. "The benchmark is applied unless there are other contributing factors that need to be considered in the development of the plan for the child and family."

He said the $16,000 price benchmark was for an annual program of early childhood therapy for youngsters with high needs and was based on "what is currently considered good practice in relation to the supports likely to be appropriate to the individual".

He said there was no cap on funding, which could be reviewed in terms of the amount of support and the period of support.