There is a correlation between child rearing and benefits-seeking (at least in the UK). Your costs appear to go up exponentially in this instance, however the benefits don't always follow.
Also, some parts of the UK are significantly cheaper than others -- i'd argue that you might be successful keeping yourself stable in the north or middle of england, but you'd struggle in london or it's outer reaches.
One more thing- people don't 'opt' to be in this situation usually, so they are quite likely to enter into it with a reasonable chunk of unsecured loans and such that'll suck up the money.
So, sure. You can be a college grad who's not yet got anything but student loans, and happily enter in to benefits to support you whilst you build something interesting... But as soon as you need to go anywhere or spend any money to further your goals, you might find yourself pretty stuck.