Taking in a grandchild has split up the marriages of one in every seven New Zealand couples who have had to do this.

A survey of 205 members of the Grandparents Raising Grandchildren Trust found that 28 marriages broke up as a result of taking in a child - 13.7 per cent of the 188 people who answered this question.

One grandmother told researcher Jill Worrall: "Just recently after 38 years of marriage we separated, and caring for a grandchild may have partially contributed to this."

Another told her: "My husband of 36 years had no patience with the children so it was either him or them and I chose the children."

That grandmother explained: "It was hard but there was really no choice [what they had come from]."

The survey found that children came into their grandparents' care because their parents were drug addicts (42 per cent), neglectful (37 per cent), alcoholics (26 per cent), or suffered domestic violence (25 per cent), mental illness (23 per cent) or other problems such as imprisonment, physical illness or prostitution or poverty.

Many parents had more than one of these problems.

Mrs Worrall, a research associate at Massey University, said 57 per cent of the grandparents had to change their work patterns when they took in grandchildren, either working fewer hours so they could care for the children or longer hours so they could pay for them.

A tenth had gone back to work from retirement to pay for the children, but still struggled to make ends meet at a time of life when income usually falls and health costs rise.

One grandmother said: "I go without food to feed my grandson, also clothes, haircuts. I can't do volunteer work because we look so raggedy away from children's activities [paint-stained clothes etc]."

Another couple had had to sell their retirement home, cash in all their savings and were "now broke".

Christchurch grandparents Gwenda and Graeme Swinney, both now 70, have brought up two grandchildren now aged 18 and 14 as well as helping to care for the children's mother, an alcoholic. Another child of the same mother is being brought up by an aunt.

"All the children come with traumas," Mrs Swinney said.

"Even if there are no real big hassles, it's just having to live with an old grandmother and an old grandfather. Our values are just so different.

"When we were 18 we had to be home at midnight. Now they only go out at midnight. We get phone calls at 2am to 'come and pick me up now'."

Their 18-year-old grand-daughter Amy represented New Zealand at a foster care conference in Ireland in July and now wants to set up a group for children being brought up by their grandparents.

Wellington grandmother Terry Ututaonga, 54, and her husband have taken in two grandsons aged 11 and 8 even though both grandparents are still working.

"You just have to re-evaluate everything," she said. "My daughter was in an inappropriate environment. There were mental health issues. My husband and I couldn't not take the kids."

Delegates at Grandparents Raising Grandchildren's first national conference in Auckland yesterday complained that many had been refused unsupported-child benefits.

Work and Income official Lynda Smardon apologised for the way some grandparents had been treated.

She said the unsupported-child benefit was not affected by the grandparents' income or whether they were on other benefits themselves.

But they did have to prove there had been a "family breakdown" which meant the parents could no longer care for the children.