The survey also found that six out of 10 of those parents that did receive support questioned its worth.
Around nine out of 10 said they encountered significant barriers when looking for mental health and emotional wellbeing support for their children.
Lack of available services, long waiting lists and children not fitting criteria for support were among the barriers listed. Some parents were even blamed for their child's problems when they asked for help.
YoungMinds is calling for awareness among GPs of the emotional needs of children with disabilities. It says councils and health trusts should set up parent support groups and children with complex needs needing support should be fast-tracked.
Claire Usiskin, the charity's parents helpline policy manager, said: "These families are among the most disadvantaged in the whole population. Their children suffer anxiety, behavioural problems and depression, in addition to physical health problems and learning difficulties.
"They have multiple, complex problems, yet still face a ‘blank wall' when seeking help. Services need to be improved fast to meet their needs."
One of the parents surveyed said: "Social services need to be able to react when problems are still small, not to wait until it has been worked up into a major issue. I don't know if it really is due to a lack of resources or the mindset of wait and see, but it's wrong and people suffer."
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Parents of disabled children lack mental health support
A third of parents of disabled children say they are getting no support with their children's emotional or mental health problems, according to a survey by the charity YoungMinds.