Some service users, the survey showed, began using alcohol at the age of 12 and were using drugs such as cannabis by the time they left school in their mid-teens.
It further found more than 71% of those questioned had, at some stage, had suicidal thoughts and more than half had a history of self-harm.
Cork Simon conducted the survey to help improve its own services for people seeking its help.
Sophie Johnston, campaigns and communications co-ordinator, said many homeless children at present are already experiencing a significant adverse childhood experience (ACE) in the form of insecure housing.
The survey was a collaboration between Cork Simon, the School of Applied Psychology at UCC and the HSE’s Adult Homeless Integrated Team.
It found 77.7% of those questioned had experienced four or more ACEs, with a score of four or more on a scale determined to put a person at a significantly increased risk of poor health and well-being.
Just over three-quarters of the service users questioned had experienced verbal abuse, 67% had suffered physical abuse and 35% had suffered sexual abuse.
The survey also showed more than a quarter of service users had endured physical neglect when younger, just under half had lost a parent and 43% had a mother who was a domestic violence victim.
In 71.4% of cases, there had been substance abuse in the family, and mental health was an issue in the family home in 59% of cases, while 67% of those questioned had suffered emotional neglect. Just under a third of those questioned had had a family member in prison.
Ms Johnston said: “What it is telling us is that there are high levels of neglect and trauma and very challenging upbringings for the majority of our service users and it’s something that people working in our shelter would know anecdotally.
“It challenges the blame and stigma and shame that surrounds homelessness. It gives us a better understanding of their life path.”
Among the findings was one regarding physical neglect and not having had adequate food in the family home, where the percentage of service users was “significantly higher” in the 18 to 26 age group compared with older service users.
Ms Johnston said this may be a legacy of the recession, although the small number involved in the study made it hard to state that conclusively.
The findings, based on an original US ACE study which set the template for its use in other areas, has resulted in Cork Simon changing its own services to ensure it is “trauma-informed”. There will be an annual review of the service and the ACE data among service users at the shelter.
Regarding current levels of child homelessness, Ms Johnston said: “If we were doing an ACE [survey] for the Irish situation, that was to be rolled out in five years time, I think it would be highly relevant that homelessness or insecure housing would be one of those ACEs.”