Indulgent parents are creating a spoilt generation with a sense of entitlement and a lack of empathy, he says.
The results are rising levels of antisocial behaviour and young people unprepared for the realities of adult life.
The father of four, brought to New Zealand by lobby group Family First, may find support for the idea of parents setting boundaries for their children.
But some of his views have been more controversial: daycare damages children, under-3s shouldn't watch television, and parents should be left to decide whether to smack their children or not.
An American who has lived in Britain for more than 30 years, Sigman speaks to the Otago Daily Times on the fly. He has just met our Children's Commissioner and is about to talk to the Families Commissioner. At times, he sounds strident, even cross.
The Spoilt Generation he refers to, in his book of the same name, are children used to getting their own way, he explains, not necessarily spoilt in terms of material possessions.
Sigman says he first became aware of the problem when publicising Remotely Controlled, his book about the biological effects of too much TV on young brains.
Several parents told him their children had TVs in their bedrooms and then asked him how they could stop their children watching so much. When he suggested removing the sets might be a good first step, he found they were afraid to do so.
Part of the issue is that we have the oldest parents in history and the lowest number of children being born, he says.
"We've never had so many sets of parents both going out working and working some of the longest hours in our history ... They feel guilty.
"When they come home, they're tired. Having to face a confrontation with a child who might want more attention is difficult and one of the ways they do this is to compensate for their guilt by allowing their child to exhibit behaviour that is unacceptable.
"You're ending up with parents who are not just afraid to say no but when they do say it, it's with a sense of apology."
Worse, some parents want to be best friends with their children.
"Of course you can't be their best friend when you're called Mummy. You don't give birth to your best friends."
Governments have given children greater rights to protect them and to make them happier and healthier, but the opposite has happened, he says.
"In a misguided attempt to democratise the parent-child relationship, they have eroded adult authority, and this has led to the harm of children and to many of the social problems we have, from drinking to teenage pregnancy to rates of depression. Children have never been so miserable and unhappy since records began."
In the United Kingdom, pupils are making an increasing number of false allegations against teachers, and children are defying authority earlier: even toddlers have been reported as being disrespectful towards nursery school staff.
Sigman says adults must be legally empowered to deal with both their own and other people's children without the fear of being prosecuted.
"If an adult sees children or teenagers beating someone up and grabs one of the teenagers roughly to try to stop them ... they can be charged with assault. And this is happening to teachers in the classroom. When a 15-year-old says, 'I'm going to stab you,' and the teacher drags them outside, the teacher's arrested for assault and loses their job.
"This isn't to say that children shouldn't have legal protection against abuse and harm from adults. But there is a shift that's happened that's caused terrible problems in Britain, and I understand ... there are some parallel things going on here."
The present emphasis on positive parenting is "inherently faulty" because parenting involves both positive and negative approaches, he claims.
"You do reward good behaviours but you also have to disapprove and show negative reactions to behaviours that are unacceptable."
Studies have shown that when there are no negative consequences, children are less secure, do less well at school and are less emotionally stable than children who have firm boundaries and stricter forms of parenting.
"This isn't to tell parents what those boundaries should be or what the consequences should be. But it's to tell parents, 'It's your duty to have boundaries, to say no and to be in charge.' I'm sorry if it doesn't feel good. And I'm sorry if it requires effort and work when you come home and you're tired. But this is a necessary issue for child health and wellbeing ..."
Sigman's critics say it is wrong to knock a whole generation of young people through sweeping generalisations: the vast majority of young people play positive roles in their communities, do well at school and are a credit to their families and themselves. He agrees but says that does not erase the fact of an increase in social problems.
He is also at pains to explain he is neither for nor against smacking: "I'm very much against outlawing parental discretion to make those decisions."
"We all want to make sure adults are arrested for beating children but I, and a lot of other people, do not believe that normal parental smacking is in any way connected with violence or beating.
"There isn't a continuum where you start off with a swat and end up with a punch in the face. That isn't the way real parenting happens."
His views on child care are equally forthright, and at odds with a new study by New York's Columbia University School of Social Work showing mothers can return to work months after the birth of their child without the baby's wellbeing suffering.
Sigman says at least 11 studies have shown being in daycare raises the levels of cortisol - a marker for stress and inflammation - in children, but academics are frightened to talk about this in case it is seen as "women-bashing" or an attempt to make working mothers feel guilty.
As for television - the medium that sparked his thinking about parenting practices - recent research has only strengthened his feeling that we should limit children's time in front of the screen.
Computers have been linked to a reduction in maths and reading ability, suggesting technology should be introduced in schools later and used judiciously or it subverts the very intellectual qualities we are trying to cultivate, he says.
Research also shows that when children watch TV, their metabolism slows, their appetite increases and there are changes in the hormones that control insulin.
Sigman adds these effects would occur whether children were watching "porn or National Geographic".
