Tory leader David Cameron has called for more powers to "compel" fathers to look after their children in an effort to tackle gang culture.
He said he backed tax breaks to help families stay together and promoting a "culture of responsibility and respecting authority".
The comments follow the fatal shootings of three London teenagers.
But Prime Minister Tony Blair said the killings were not "a metaphor for the state of British society".
Mr Cameron called for a "complete change in our values".
He said: "I believe in marriage. I believe in people making a commitment to each other and staying together and trying to bring up their children properly."
Children were often attracted to gangs if they lacked a father figure, he added.
Mr Cameron said: "We have got to sit up and realise we are running things by the wrong values. We need to support families."
The Child Support Agency was "meant" to collect money from fathers to pay for raising their children, but men in other European countries faced "tougher rules and had to stand by" their families, he said.
A Unicef report published this week put UK children at the bottom of a well-being league table of 21 industrialised countries.
Mr Cameron told a youth organisation in Oxfordshire this meant society was in "deep trouble".
He said: "In the last two weeks, five people have been murdered in south London - three of them teenagers.
"On the face of it, this is a law and order issue. But surely no-one imagines that we can stop crimes like this simply with better policing or better gun control.
"The problem lies within families and communities, and so does the solution."
Mr Cameron also said: "I'm not talking about taking on a gang of dangerous thugs.
"I'm talking about treating children and teenagers with respect - with the expectation that, if they are spoken to as reasonable people, they will respond as reasonable people."
But Mr Blair said: "What has happened in south London is horrific, shocking and, for the victims and their families, tragic beyond belief.
"However, let's be careful in our response.
"This tragedy is not a metaphor for the state of British society, still less for the state of British youth today, the huge majority of whom are responsible and law-abiding.
"It's a specific problem and a specific criminal culture among a specific group of people."
Home Secretary John Reid held a meeting on Friday with MPs from south London.
'No quick fixes'
Afterwards he suggested he was looking at ways of toughening gun laws.
"I have also asked my lawyers, the home office lawyers, to look at ways of possibly strengthening legislation and where appropriate, sentencing," he said.
He said those who suggested the shootings were the result of social breakdown underestimated "the vast majority of people in this city and in this country who are not like that".
He added such suggestions should not become "an excuse, or an alibi or a justification for these dreadful, awful, terrible crimes".
Liberal Democrat leader Sir Menzies Campbell said: "There are no quick fixes to the problems of relationship breakdown and a disenfranchised generation.
"Nurturing families and building communities takes years."
After this month's third fatal shooting in south London, armed police officers are to patrol the streets as part of a new task force announced by Metropolitan Police Commissioner Sir Ian Blair.
Billy Cox, 15, was found dead by his 12-year-old sister at their home near Clapham North underground station on Wednesday.
Michael Dosunmu, aged 15, was shot dead in the bedroom of his Peckham home on 6 February. A man has been arrested in connection with the killing.
Three days earlier, 16-year-old James Andre Smartt-Ford died after he was shot at Streatham Ice Arena.
The new task force will run alongside Operation Trident, which investigates gun crime in the black community.
Billy Cox's father Tommy said: "I've been watching news about the two other boys shot and thought - these are only kids.
"They don't deserve that. The way they get hold of guns now is unbelievable.
"I want everyone to get behind the police 100%. If you have anything to say, tell the police. We and all his family will miss him so much."