All afternoon we were bombarded with misery about childhood today: kids are lonely and unhappy, fat and bullied. Half don’t eat breakfast, a third of under-16s regularly drink, nearly four in ten 15-year-olds have had sex. About 4,000 or 8,500 children (depending on which spokesman you were listening to) were admitted to hospital with alcohol-related illness, some 630,000 prescriptions for antidepressants are handed out to children annually and 11.2 per cent of girls self-harm.

Their dads are missing, their mums are working (or not working, which is worse), half a million are in failing schools, a fifth are shouldering adult responsibilities because their parents are disabled, drink or drug-addicted. Welcome to the Conservative Party conference 2007, and its message of optimism, hope and change. Once the politicians had finished, a slew of invited voluntary workers stood up to plead that we offer the children of chaotic and underprivileged families hope and aspiration rather than condemnation and pessimism.

And the solution from the Tories? More outside play. That was the conclusion presented at the end of Monday’s long and miserable session by the man asked by David Cameron to conduct “an inquiry into childhood”, David Willetts. In his earlier guise as Shadow Education Secretary, Mr Willetts was coming up with some challenging stuff about how quickly social segregation is entrenched in the early years, before kids even get to school, because of the ruthless ambition of the middle classes. That effort saw him removed from the education brief to a quieter place. Now, in a decent but hardly earth-shattering piece of work, he talks about the need for more playgrounds. The Conservatives’ childhood agenda has shrunk from revolution to roundabouts.

At least he isn’t doing any harm with that. I wish the same could be said for Mr Cameron’s other “childhood” policy, rewarding couples with children with extra tax credits. Mr Cameron appears unable to see what every other numerate person can: his plan is rubbish.

It is not the case that couples who stay together are penalised and paid less in working tax credits than lone parents, an error parroted by people who are too well paid to know. Both families get the same. The Tories have been using a grossly misleading comparison, first cited by the Labour MP Frank Field, to back up their case. Mr Field has said that a single mother working 16 hours a week, after tax credits, gains a total income of £487 a week, but a two-parent family earning the minimum wage has to work 116 hours to gain the same income.

If you take childcare and housing costs out of it (for some reason Mr Field put the lone parent in rather expensive private rented accommodation, which is totally unrealistic), the lone parent in fact has £209.49, but the couple has £309.18 net income. Look at any honest statistics: single-parent families are far more likely to be poor than two-parent families.

The only problem addressed by Mr Cameron’s policy is this: if you are a couple with children living together, but you lie about the fact, then you are up to £1,700 a year better off from the working tax credit, as one of you can claim a lone parent top-up. This encourages people to lie about their living arrangements when they claim the tax credit. So Mr Cameron wants to offer the extra £1,700 to couples with children who admit to living together. That’s it. At most it will stop some low-earning couples who live together but lie about it from lying about it in future.

See? It doesn’t make any sense as a “boost for marriage”. You don’t have to get married to be eligible. And if you are already married, well, you don’t need the encouragement then, do you? You’re just being given an extra £30 a week. Nice, but why? If you want to raise children out of poverty, as the Tories claim, then putting extra money into working tax credit for couples is about a third as effective as putting it into more child tax credit for all children, according to the Institute for Fiscal Studies.

Mr Cameron’s policy is unfunded. It will cost an estimated £3 billion a year, a penny on the basic rate of income tax, no mean amount to play around with. There isn’t even any evidence that it will be effective: tax breaks for marriage in the 1970s and 1980s coincided with a steep rise in family breakdown. So its only value is a symbolic one: to signify that Tories believe in two-parent families. Yet the recent Unicef report into childhood found children to be happiest in the Scandinavian countries with among the highest rates of lone parenthood in the world: it doesn’t have to make kids unhappy; inequality does.

No wonder lone-parent campaign groups have been alarmed. This would appear to be a shift back towards the days when senior Tories thought it was OK to stigmatise and discriminate against single mothers – that’s nearly two million parents raising more than three million children: one in four of all kids.

I wonder if Mr Cameron knows who these people are. The median age of a lone parent is 36 (only 2 per cent are teenagers and less than a quarter are under 30), half were previously married, a tenth are men. I was thinking about the three lone-parent families I know locally. One is a widow who had three children under 5 when her husband died. Another is a divorced man whose son chose to live with him, not his former wife. A third was left by her husband when she was pregnant. All of them work. Their childcare arrangements are fiendishly complex – and expensive. Their average age is over 40. Why these people should deserve less help than a couple raising children together is beyond me.

But I’m sure they will be delighted when I tell them that it’s OK because Mr Willetts is going to build more playgrounds.

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