The figure is down 150,000 from a year ago, Jiji Press reported.
The population of children has declined for 32 consecutive years since the government began keeping records in 1950.
The proportion of children relative to the overall population is now at 12.9 percent, which is the lowest figure among countries with populations over 40 million, the data indicates.
The U.S. children to population ratio is 19.6 percent and China's is 16.5 percent, Jiji Press reported.
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