An Auckland mother says her close relationship with her two sons quickly disappeared when her marriage broke up.

It came as a surprise to her, as she had been their primary caregiver and doted on them. The father had been distant from the kids before they broke up in 2015.

"Up until we split he was almost a disinterested parent," the mother said.

"My youngest son is a very good soccer player. And his dad would say 'F*** off, I'm not coming to watch you play a sissy game'."

The woman - who cannot be identified because the case is before the Family Court - said her ex-partner took a sudden interest in the boys, aged eight and 11 at the time of the breakup.

"He just completely turned the boys against me. I went from being a really involved, much-loved parent to suddenly I was the devil incarnate.

"He would say to them, 'Your mum doesn't love you, she is mental, she will hurt you'. It's sometimes more subtle, insidious messages that you can't even put your finger on.

"If my boys came to me with bruises, then I could say to the doctors - 'look'. But because their bruises are mental it is so much harder to deal with."

She initially lost the custody battle but later won the right to see them again once or twice a week. But the damage has been done, because the boys now despise their mother.

"Family courts really don't seem to know how to deal with parental alienation," she said.

Research has shown that parental alienation has widespread and serious negative effects on children later in life.

A new University of Otago study by Nelson-based solicitor Lee James, published in the New Zealand Family Law Journal this week, says reforms of the Family Court are needed to deal with the issue.

James, who has practised family law for 20 years, said parental alienation was one of the most challenging problems she and her colleagues dealt with.

"It's about the child rejecting contact with the other parent but as a result of the behaviour of the alienating parent.

"And generally, it is when the child has had a positive relationship with the targeted parent."

Alienating behaviour includes one parent making negative comments about the other parent, limiting contact or communication, getting upset if a child is affectionate towards the other parent, expecting the child to choose between one of the parents, asking a child to spy on the other parents, or making the child feel bad about spending time with the other parent.

This could cause depression, insecurity, reduced self-esteem, gender identity problems, and mistrust among children, James' study said.

She proposed two main changes to the Family Court. The first would be the ability to identify alienation and its causes. And the second would be the ability to get more help for children in such cases.

Research had shown that there was a close link between severe alienation and personality disorders in the parent who was responsible for estranging the child.

"Earlier identification by way of psychological assessment would certainly make it easier and improve outcomes for children if that can be dealt with," James said.

Under existing law, assessments can already be ordered for children in the Family Court, but not for adults. However, parents are usually responsible for a child's alienation after a relationship breaks down.

There were also no measures in current laws to direct counselling for a child or reunification with a parent, James said.

Reforms of the Family Court by the previous National-led Government in 2014 removed judges' ability to order counselling for children.

There were some challenges in the proposed reforms. Some children were "justifiably estranged" from parents because of violence, abuse or neglect, James said.

She believed that her recommended changes would help to assist in these cases, which often consumed huge resources in the courts.