aRE you celebrating Universal Children's Day? What do you mean you had no idea it was happening? If you're a parent, every day is probably children's day. Noisy children's day, cute children's day, messy children's day and so on. If you're a 30-something woman who remains childless, like me, Children's Day has probably set you wondering if there's enough time to create a Walton's-style brood of loveable offspring.  Ever since the UN announcement a few weeks back that the world's population has swollen beyond seven billion, talking heads galore have been wading in with their tuppence-worth about the connection between population and the environment. My interpretation of their combined natterings is that it's not the big families of developing countries that pose the real threat to the planet, it's the resource-guzzling little misses and misters of the West. This notion is fuelled by studies that show having a child is the naughtiest thing you can do in terms of a carbon footprint.  Two years ago, research by the Oregon State University concluded that in the USa, the greenhouse gas impact of a child is 20 times more influential than any other factors, such as driving a gas-guzzling vehicle. These sorts of stats have led some environmentalists to proclaim that they will remain child-free so as not to f