The Nappy Valley of South-West London is situated right between Wandsworth Common and Clapham Common. Nappy Valley is exactly that, a valley, with Northcote Road at the very bottom. It was named so by the London Evening Standard.

Called Nappy Valley because, apparently, all the young families who live there took their inspiration from the Baby Boom Generation and just kept on booming. This area has the highest density of children in Europe, the highest teen conception rate (63.6% of the 15-17 year olds living in Nappy Valley get pregnant each year, and 14.9% of 13-15 year olds) in England, and one of the highest overall conception rates in England. Mywandsworth.co.uk says this;

"There's no shortage of cafés filled with lunching ladies and screaming babies along the 'nappy valley' that is Northcote Road."

Upsides to living in Nappy Valley?
Nurseries and shops that cater for babies.

Downsides to living in Nappy Valley?
The severe shortage of babysitters, and so forth.

There is also a nappy valley in Australia, and I'm not sure where else? Write-ups!