Government must no longer "shy away" from acting to keep families together in a bid to stop children ending up in poverty, in prison or jobless, the Prime Minister is to say.
David Cameron will use a speech to pin the blame for many social problems on "bad" personal relationships and reject suggestions that ministers are powerless to intervene.
As part of his stated aim to make Britain "the most family-friendly country in Europe", he will insist it is right to target relations between parents.
Addressing the Relate charity, Mr Cameron will deny looking for "nanny state" snooping in personal lives or attacking unmarried couples, single or same-sex couples.
But he will call for an end to the "defeatist" attitude which said there was little government could do to help promote strong families.
Extracts of his speech released by Downing Street contained no detailed policy suggestions but promised "thoughtful, sensible, practical and modern support".
He is expected to say: "When parents have bad relationships, their child is more likely to live in poverty, fail at school, end up in prison, be unemployed later in life. It would be wrong for public policy to ignore all this."
He will continue: "For years, government hasn't talked about families, hasn't understood the importance of support at the vital times, hasn't valued commitment.
"And that's why it's been guilty of adding to, indeed at times creating, an environment for relationships which is all too often incredibly difficult.
"If we're serious about supporting families, this is what needs to change."