SHANGHAI  -- The number of only children in China has surpassed 100 million since the introduction of the one-child policy in the late 1970s, according to a population forum here on Sunday.

The single children group accounted for about 8 percent of China's 1.3-billion population, according to the forum hosted by Shanghai Population Welfare Charity Fund ahead of the July 11 World Population Day.

Families have become smaller and smaller since 1982 when households averaged about 4.4 members. In 2005, the figure was reduced to about 3.1.

The "core family," which consisted of a couple and one child, had become the common family pattern in Chinese urban areas, the forum said.

The one-child policy has prevented an estimated 400 million births.