Families celebrate Children's Day at a park in Beijing. Children's Day, an annual holiday since 1949, is an important event for a country where most families have only one child. See more pictures of Beijing.

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There are more than 1.3 billion people living, working and building families in China. Until a century ago, many Chinese families included multiple generations living under one roof. Today, though, it's no longer the norm.

These days, a typical Chinese family includes a married man and woman with one child, referred to as a core family. While there are some instances when a core family may look a little different, such as when a family is caring for one or both sets of grandparents, the percentage of core families continues to rise above other types. This rise is no coincidence -- it's a direct reflection of the Chinese government's population control policies.

The National Population and Family Planning Commission of China (NPFPC) is a state agency responsible for overseeing population control, reproductive health and family planning across China's provinces, autonomous regions and municipalities. In this regard, the agency crafts policy and legislation, organizes and coordinates publicity and education, and directs and supervises reproductive science and technologies. The NPFPC limits the number of children Chinese couples may have, commonly known as the one-child policy.