Dave,
Historically, the government has always encouraged us 'plebs' to do the stuff they want us to do via the tax system.
The government WANTS us to have kids. Given that we have an ageing population, our kids will turn into the 'money makers' of the future and pay for our pensions.
Also, kids born into poverty aren't as healthy, bright, or well-adjusted as those from more affluent families (usually).
So families with kids get financial help from the state!