On any given night, there are about 35,000 homeless people across Canada, and the number of families and children among them is growing at an alarming rate, a new report reveals.

One in every seven users of homeless shelters is a child, according to Putting an End to Child & Family Homelessness, being published Monday by the advocacy group Raising the Roof.

The report shows that family use of shelters has jumped 50 per cent in the past decade, and their length of stay has increased markedly in recent years to an average of more than 50 days.

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Further, nightly shelter use is just the tip of the iceberg. About 235,000 people used homeless shelters at some point last year, and that doesn't include the "hidden homeless" who crash with family and friends, or live in their cars.

All told, about 3.1 million Canadians are precariously housed, living in crowded, sub-standard housing or in unaffordable housing (meaning more than 30 per cent of their income goes to housing costs), and many of them are one rent payment away from homelessness.

"The older, single white men we see on the street are the most visible homeless, but family homelessness – including children and youth – is a significant part of the crisis," said Carolann Barr, executive director of Raising the Roof.

She said there is rarely a single reason people become homeless, but poverty is often the driving force: Far too many families have to make a choice between paying the rent or feeding the kids.

Not having a home is particularly challenging for children because of their needs for schooling and health care, and because they often lack other basics of life like proper nutrition, adequate clothing and a safe environment, that will have a lifelong impact on their health and well-being.

There is also a significant impact on their mental health, so much so that Raising the Roof published a supplementary report entitled Child & Family Homelessness: A Determinant of Children's Mental Health.

"Children are particularly vulnerable to homelessness and the underlying causes of homelessness like lack of income and family violence," Ms. Barr said.

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The rate of depression among homeless mothers is 45-80 per cent, which is four to five times higher than the general population. One in three homeless mothers has also made at least one suicide attempt.

That obviously has an impact on children, who themselves suffer high rates of depression, post-traumatic stress disorder, eating disorders and anxiety disorders.

Ms. Barr said homelessness itself can be traumatic, but so too is being a victim of violence, or even a witness. Precarious living conditions also make it more likely children will be victims of sexual abuse and of physical injury from living in unsafe environments.

"When you're worried about day-to-day survival, it's hard to address your mental-health issues, or your kids,'" Ms. Barr said.

Domestic violence is one of the leading causes of homelessness among families, when women flee abusive relationships. The report notes, however, that families and children living in shelters for victims of violence are not included in homelessness data.

Much of the new report focuses on the fact that there is inadequate effort to prevent homelessness.

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It recommends that federal, provincial, territorial and indigenous governments join forces to create a national housing and homelessness strategy, as well as a national poverty reduction strategy that focuses on families and children.

It also calls for the creation and funding of a national co-ordinated action plan for addressing children's mental health, one that includes measures related to homeless children.

Ms. Barr said it's "quite urgent" that prevention measures be implemented to tackle Canada's growing problem of homelessness and unaffordable housing.

But she also stressed that, despite the magnitude of the challenge, she is actually optimistic because "there are a lot of great programs out there and a lot of momentum to co-ordinate and create and implement a national plan."