The plans are set out in a report from Iain Duncan Smith's think tank
Pre-nuptial agreements would be legally binding and cohabiting couples refused the same rights as those who wed, under plans from a Tory think-thank.
The measures, aimed at strengthening marriage, would also improve access to children for fathers and grandparents.
The interim report is from Iain Duncan Smith's Centre for Social Justice.
The former Tory leader said tackling "dysfunctional, broken family life" was critical if abuse like that suffered by Baby P was to be reduced.
The 17-month-old's death in Haringey, north London, after months of abuse has prompted several inquiries. His mother and two men have been convicted of involvement in his death.
Mr Duncan Smith said the publication of the interim report was "timely" given the case: "If you look at the sort of families where there is this level of abuse is taking place, you will find they are all essentially broken families."
He said the care system had become "overloaded" - the number of children being taken into care had risen by over 20% in 10 years, yet the system itself was in crisis.
Many children taken into care ended up with "worse life chances" - he said a third of the prison population was made up of people who had been in care.
"The whole system needs looking at but you have got to get to the root cause of this - which is this very high level of broken homes and dysfunctionality which takes place which is hugely damaging to our children."
Mr Duncan Smith chairs the Tories' Social Justice Policy Group as well as being the founder of the think tank Centre for Social Justice, which produced the report.
It advocates using the law and other official mechanisms to discourage "informal" relationships, and links rising levels of family breakdown to the increase in cohabitation.
He said it worked from "an underlying assumption that marriage should be supported both in government and in the law".
"Policy can and should be focused on stemming the tide of relationship breakdown. Marriage acts as a stabiliser and a signal.
"Married couples are far less likely to break up than couples who live together without getting married."
The document backs the establishment of "family relationship centres", modelled on those found in Australia, which can help separating or divorcing couples.
It is opposed to greater rights for cohabiting couples, which it argues are "not compatible" with encouraging marriage.
None of the ideas are firm policy suggestions for the Conservatives - and even if Mr Duncan Smith did include them in a policy group report they would not be binding on current leader David Cameron.