May 5 (Bloomberg) -- The number of children in Japan fell for the 27th straight year as a declining birth rate erodes the financial security of the world's most rapidly aging citizenry.

The number of Japanese younger than 15 dropped 0.7 percent from a year earlier to 17.25 million as of April 1, the nation's Statistics Bureau said in a statement yesterday. Children are a record low 13.5 percent of the population, down from 13.6 percent.

A shrinking pool of workers and taxpayers in the world's second-largest economy increases the burden on the government to fund its pension system and repay debt. Japan has the world's highest ratio of people older than 65.

In the U.S., 20.3 percent of the population is under 15, according to the Statistics Bureau. That compares with 19.4 percent in China, the world's most-populous country.

To contact the reporter on this story: Naoko Fujimura in Tokyo at nfujimura@bloomberg.net.

Last Updated: May 4, 2008 22:40 EDT