And they didn't live happily ever after.

Once upon a time, there was a mother pig who had three little pigs. The three little pigs grew so big that, one day, their mother said to them, "You are too big to live here any longer; you must go and find houses for yourselves".

If an article in one of last week's (paywalled) papers is to be believed, this scene is being played out on a regular basis up and down the country, with young people told to move out of the family home because 'their bedrooms are needed for younger siblings'.

The implication was that the withdrawal of housing benefit for the under-25s would cause great hardship for this reason, which rather suggests that their families were expecting the state to provide a safety net - and accommodation - once the 'child' reached 18, making way for more children in the household.

For those in receipt of the maximum amounts, child benefit and child tax credit combined can represent a significant proportion of the household income. It's a laudable practice when it enables a responsible family to meet their bills and feed and clothe children who might otherwise go hungry but there is a fatal flaw in its application.

In its simplest form, child = income. While those who bear the full financial responsibility for their offspring might hesitate before adding to their brood, there is no financial disincentive to produce large families when someone else is footing the bill; science has long known that mammal populations expand in times of plenty and humans are no exception.

And, just as in the animal kingdom, that expansion brings an increase in predators trying to benefit in their turn. Along with the tattoo artists, beauticians, baby boutiques, high street bookmakers and lottery ticket sellers are men who batten onto young single mothers to profit from their accommodation and child benefits.

This may well be the untold story behind the cohort of newly-homeless teenagers; a mother infatuated or dominated by a potentially hostile partner is surely far more likely to follow her primitive animal instincts to protect and nurture his new offspring and pack the previous litter off into the wilderness to fend for themselves. Like the starry-eyed progressives who wrecked our education system, those responsible for the tax credit structure appear to have ignored the animal instincts that drive human behaviour.

Suggestions of denying payment for children conceived  by parents already on benefits have led to much outcry (and an assortment of straw men - or rather women), as you would expect to happen with a system that allows claimants to generate their own hostages. The Dickensian spectre of child poverty makes a powerful argument; so powerful, in fact, that it appears to have obscured the question of how many children there are and what happens to them when they grow up.

While the vast majority of parents will doubtless continue, as generations before them, to support, house and occasionally be driven to distraction by their grown offspring until they achieve independence, there is a danger that a proportion of teenagers who cease to qualify for child benefit and tax credits will suddenly find themselves evicted from the family home while still young enough to be vulnerable to every passing Big Bad Wolf.

I don't have a solution, though it would certainly help if people could be persuaded to take a more responsible approach to parenthood; in a country where pets are acquired on a whim and abandoned at will, I can't imagine the families in question ever taking on board the idea that a child is for life, not just for tax credits.