Mr Cameron wants to de-stigmatise relationship support
David Cameron says a Conservative government would strengthen the role of families - to counter social breakdown, crime and anti-social behaviour.
He said they would put tax breaks for married couples, help for troubled relationships and affordable childcare at the centre of "social reforms".
The UK would never get to "the heart of the problems we face" without providing more help for families, he said.
But Minister Beverley Hughes dismissed the measures as "shallow showmanship".
Her comments follow a warning by watchdogs that children risk being "demonised" by society.
The report from the UK's Children's Commissioners claims Britain's children feel increasingly unsafe, drink more alcohol and face more pressure at school than elsewhere in Europe.
In a speech at the relationship guidance charity Relate, Mr Cameron argued that the family is "the best institution in our country" to "strengthen our society".
"Right now Britain has one of the highest rates of family breakdown in Europe - and we also have some of the worst social problems in Europe," he said.
It was time "to make this country more family friendly", by turning around social breakdown, crime and anti-social behaviour and the "unacceptable situation where our cost of living's going up and the quality of life is going down".
"I don't think we'll ever get to the heart of the big problems we face, from crime and anti-social behaviour to welfare dependency and educational failure; from debt and drug addiction to entrenched poverty and stalled social mobility, if we don't help the best institution in our country - the family - do the vital work that it does in bringing up children.
"What that help is - and how it is delivered - will be amongst the defining social reforms of the next Conservative government."
Mr Cameron conceded that politicians, with their reputation for affairs and divorces, are not always the best role models.
"Some might say the best thing politicians can do is 'keep their noses out', but I think that's a bit of a cop out," he said.
Social breakdown costs an estimated £20bn, yet the annual budget for Relate, which helps keep families together, is only £24m, he pointed out.
It is essential for governments to support the family and keep couples' relationships intact, he said.
"I want to de-stigmatise relationship support so people feel completely comfortable, if they have a nagging difficulty in their relationship, in getting help from organisations like Relate," he said.
"Government can take a lead here. One way is to start early - and insist for example, that there's no sex education in schools unless it includes relationship education."
Mr Cameron said it was wrong that the benefits system gives couples with children more money if they live apart and does not properly recognise marriage in the tax system.
But Ms Hughes, minister for families, accused the Tory leader of having "no credibility on supporting families" when he voted against parents having the right to request flexible working, longer paid maternity leave and paid paternity leave.