Re: The child sized elephant in the room @Richard 12
No, we really don't need an average family size below 2. One-for-one replacement in the global population as a whole, yes, but...
Because of lifestyle choices and mortality, if you're talking about the average 'family' - defining a family as a social unit that includes kids, which would exclude people living on their own or couples not having children, the average family size needs to be between 2.3 and 2.4 children in the UK to achieve a stable population. In other countries with higher mortality rates, it could be higher.
The current plan to eliminate child benefit in the UK beyond 2 children will actually detrimentally affect the demographics of the country, IMHO.
<contentious><generalised>The financially responsible families, who are most likely to have children who grow up to be like them will be choose to keep their family to two children (or if they're real do-gooders, to just one child). The families who have a have children now and worry about how they're going to raise them later mindset will not really care, and will still expect state support. Kids tend to grow up like their parents</generalised></contentious>.
The effect on the population could result in the rise of a new 'chav' generation, skewing the population towards under achievers, hangers on and people with an expectation that the state will take care of them. Exactly what is not required.
I know that I'm generalising, but in general most developed countries have a population stability problem, with some countries like Japan actually having a declining population some time back.
What the world really needs is sensible population control policies, together with education to back up these policies, targeted at all countries, especially those with the highest population increase. It won't happen, as the UN charter actively prevents one country from interfering in another countries internal affairs, and the countries that most need the control are the ones least likely to implement or accept it.