New step-parents who jump in and act like real parents are asking for trouble, claims a new study.
Auckland University researchers have found that children are more likely to want their step-parent to be a "friend" than a "parent", and want their biological parent to stay in charge of discipline.
It may sound like common sense. Yet Dr Vicki Mobley, a clinical psychologist who has just completed her doctorate on the issue, has found that parents and step-parents still want to create a more traditional "nuclear family" pattern.
Three-quarters of the 40 adults she interviewed in step-families wanted step-parents to share actively in disciplining the children, even though they found this difficult or impossible.
About 20 per cent of New Zealand children live in step- or blended families, so Dr Mobley and her academic supervisor, Dr Claire Cartwright, believe there is an urgent need for more education and support.
"They are going to face quite extreme challenges in the first, probably two years," Dr Cartwright said.
"It would be better if you are going into it with your eyes open, to know that children have difficulties with the adjustment, and it works better if you take it slowly."
She found that many of the 99 step-parents in her study were unprepared for their new role.
A third moved in with their partner after less than six months and almost two-thirds within a year.
But only 40 per cent said they talked about it "a lot" with the children first, 36 per cent said they talked "a bit" and 24 per cent said they "did not talk about it as we thought it would go well".
Dr Mobley's study found that the children in step-families have different views on how step-parents should behave.
A 12-year-old girl said: "The step-parent should do nice things with the kids and do that the same all the way through. But the discipline should be less at the beginning because you don't know each other well."
Even on non-disciplinary matters, the children didn't want their step-parents to get too close. A 14-year-old girl said children didn't like a stepmother "smothering them and not giving them any room".
Dr Mobley concluded that a close "alliance" between children and one biological parent was normal in step-families, even though it would be seen as dysfunctional in traditional ones.
The step-parent's best role might be to do practical and fun things with the children and support the biological parent.
'I suddenly took it very seriously... '
Stepfather Simon Darcey says his biggest mistake was to take his new role too seriously.
Mr Darcey, a North Shore IT consultant, moved in with the woman who is now his wife, Jill Darcey, when her children were aged 11, 10 and 8.
Unlike many, they had prepared for the change. They met at first on Wednesday nights and weekends, when the children were with their father.
They took the children on picnics, then on camping trips, so they got to know Mr Darcey before he moved in after 18 months.
Mr Darcey feels now that he made mistakes when he moved in.
"I suddenly took it very seriously - this is a huge responsibility, I'd better stop clowning around being the fun guy. So I reduced the humour and increased the intensity."
After a year or two he and Mrs Darcey were clashing. "So I had to try to reverse that again."
Mrs Darcey has written a book about her experience and lessons from other parents with new partners, Parenting with the Ex Factor.
What adults want to be
Step-parent: 44 per cent
Parent: 32 per cent
Friend: 10 per cent
Aunt/uncle/other: 14 per cent
What children want
Step-parent: 29 per cent
Friend: 26 per cent
Aunt/uncle/other: 24 per cent
Parent: 21 per cent