According to Japanese mythology, on the 7th day after the death, on the way to eternity, the soul must cross the Sanzu river. Depending of its karma, the soul will have to pass over a wooden bridge or through the water infested with demons.
Since the dead children had no time to live and collect good deeds, they wouldn't be able to cross the river and they would be forced to stay for eternity near the river, building stone towers as a penitence. But Jizo comes and save them, crossing the river with the children hidden in his robe.
That's why you will find many Jizo statues in Japan with small piles of stones in front of them. The stones are placed there by the grieving parents, praying to Jizo to save the souls of their children...
EXIF info:
Nikon D300
Lens: 18-70mm F/3.5-4.5G
Focal Length: 18mm
Aperture: F/3.5
Shutter Speed: 1/80s
ISO Sensitivity: ISO 200