Free Exchange over at The Economist website is discussing the role of government policy in influencing fertility. They argue that if governments want to influence people to have more children, they should spend more on roads to foster a suburban lifestyle.
I would conjecture that causality is exactly the opposite: people with children sort themselves into suburban areas and not that suburbia makes people have more children. The effect is similar to how fat people sort themselves to suburban area as shown in this study.
Don't expect a baby boom to coincide with highway spending.