The study of 1,192 parents from across England also found that two-thirds of families found it "difficult" or "very difficult" to find appropriate childcare for their disabled child during summer 2011. This meant that one in three disabled children received no childcare over the summer holidays.
The survey asked parents about their ability to maintain employment and look after their children.
Although 19 per cent of those questioned were able to maintain a full-time job while caring for their disabled child, 41 per cent said they need childcare to be able to work and 43 per cent said they were unemployed due to a lack of affordable, appropriate childcare.
Kids and Mencap are now calling on local authorities to improve childcare provision to meet the requirements of families with disabled children.
The charities warned that around 20 per cent of parents of disabled children face childcare costs of up to £11,700 per year, compared to the national average of £5,028.
Kevin Williams, chief executive of Kids, said it is "disappointing, but not surprising" that so many families were unable to access childcare for their disabled child this summer.
"Caring for disabled children without the right support can have significant consequences for a whole family, not just a disabled child," he said. "The effect can be profound: disabled children lose out on opportunities to socialise with peers, relationships between parents can become strained or even break, and siblings or other family members may take on additional caring responsibilities."
David Congdon, Mencap head of campaigns and policy, added: "We know that families with a disabled child have many additional costs associated with their child’s care. Compounding this, parents face a real struggle to juggle caring for their disabled child and finding and maintaining full- or even part-time employment.
"Local authorities have a duty to provide sufficient childcare, which should be a universal service. Too often families of disabled children are let down."
