Now in their seventies, they'd like to enjoy a well-earned retirement.

Instead, they find themselves rallying on the steps of parliament and drafting complaint letters. Pleading - yet again - for certainty.

They're part of a group of Victorian parents who have launched a state-wide campaign against the Andrews government's plan to "privatise" state-run group homes, where their adult children with disabilities live.

These parents say there is no evidence this change will benefit residents - some of the most vulnerable people in the state - and fear the quality of their care will plummet.

"The government's decision to dismantle this system is causing considerable stress and anxiety," says campaign member Phil Lipshut, who has an adult son who lives in a group home.

"We strongly believe this will mean an exodus of staff".

In Victoria, the government runs 500 group homes for about 2500 people, many with cognitive disabilities and complex health conditions.

A similar number of homes are run by private and non-government organisations.

Staff in government homes are better paid and less casual staff are used than in private and not-for-profit counterparts, which have been historically underfunded.

With the introduction of the National Disability Insurance Scheme (NDIS), the Minister for Disability, Martin Foley, has called for expressions of interest from non-government organisations to take over state-run homes.

Mr Foley says the NDIS will offer "choice and control" for people with disabilities and has assured parents there will be no "transferral" unless providers can show they are financially viable and have a strong safety record.

But parents such as Robin and Bernard, whose children have lived in both systems, are not convinced.

Their son, who sadly died in 2003, lived in a privately-run group home where there was high staff turnover.

Because of this, their son (who they do not want to identify) wasn't able to form close bonds with staff.

"We feel very sad for him that he was not able to have this continuity," says Robin.

In contrast, their adult daughter (who has autism and an intellectual disability) lives in a department-run group home and has had the same house supervisor and key worker for seven years.

She has formed close relationships with support workers and they have been able to reduce her anxiety.

"It takes time to understand her, and know how she thinks." says Robin.

VALID, the main advocacy group that represents adults with an intellectual disability, has taken no position on the proposed change, but says group homes must provide quality care.

But there is mounting evidence that the funding the NDIS will provide for disability support services is inadequate, says VALID chief executive Kevin Stone.

"We're not anti-private; it might bring a welcome shakeup of some of the bureaucratic inertia," says Stone.

"But we want to see proof that promises will be kept in relation to quality."

The Victorian government doesn't want to shoulder the gap between what the NDIS will pay and the true cost of supporting people with complex disabilities, says Health and Community Service Union head Lloyd Williams.

"This mantra of 'choice' is just a red herring to divert attention away from their way of privatising services," says Williams.

The parent group, called REAL Choice for DHHS Disability Housing, has met with Premier Daniel Andrews and will lobby members of parliament.

In a statement, Mr Foley said the introduction of the NDIS meant the disability sector needed to expand.