Taken from Wikipedia. I knew about it because a colleague mentioned to me the night before while visiting the Tokyo Tower.
In Japan, Ksitigarbha, known as Jizō, or Ojizō-sama as he is respectfully known, is one of the most loved of all Japanese divinities. His statues are a common sight, especially by roadsides and in graveyards. Traditionally, he is seen as the guardian of children, particularly children who died before their parents. Since the 1980s, he has been worshiped as the guardian of the souls of mizuko, the souls of stillborn, miscarried or abortedfetuses. In Japanese mythology, it is said that the souls of children who die before their parents are unable to cross the mythical Sanzu River on their way to the afterlife because they have not had the chance to accumulate enough good deeds and because they have made the parents suffer. It is believed that Jizō saves these souls from having to pile stones eternally on the bank of the river as penance, by hiding them from demons in his robe, and letting them hear mantras.