But you can't just say go have babies anymore and expect them to bounce into the workforce. The Shenzhen couple thought they were rebels embodying a popular but silenced cause. Yet, other analyses suggest that the number of people who want multiple kids has declined as child-rearing costs rise and urban couples rely less on progeny for old-age care. China can still expect a baby boom as couples -- such as the one in Shenzhen -- just want bigger families for either financial security or to live out personal dreams.

But the wave of newborns wouldn't be able to work for 15 or 20 years. Economic growth is slipping today. And the pace of productivity growth is likely to slow anyway as "the room for catch-up with richer economies diminishes," Capital Economics says.

Those looking for consumption dividends from a higher birth rate should refocus to countries with better demographics, perhaps to Indonesia or the Philippines.

Credit Suisse expects 8.3 million additional births from 2014 and 2020, on top of the current 16 million births every year. Average cost per kid under 18 would be just 416,000 Chinese yuan ($68,470), which doesn't buy even a single Porsche 911. High-end brands such as BMW or Louis Vuitton hardly need to step up marketing just for these newborns.

"We think that the market may have over-estimated the number of additional babies following the easing of policy," the Swiss investment bank says in a research report.

The author has no positions in the shares of companies named in this column.

Ralph Jennings is on LinkedIn

Ralph Jennings lived in Beijing for seven years as a writer, editor, student, teacher and consumer. Originally from Portland, Oregon, Jennings has covered financial markets in Asia since 2008. His news reports often examine markets from a macro-policy angle on behalf of individual traders as well as institutional investors. In his view, China is a volatile country that can be understood only by watching it closely week in, week out, followed by analysis mixed with hands-on perspectives. He currently lives in Taipei, where he covers general and financial news in East Asia and studies for a master's degree. He also watches China from the unique perspective of Taiwan's traditional Chinese society with its unique economic and political experience.

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