The two girls, thought to be ten or 11 years old and from an Albanian family, were playing in the river in the village of Breme, in the region of Lombardy, when the tragedy struck, according to Italian press reports.
Divers recovered the body of one child on Sunday, while the other was found on Monday.
The girls were close to the river bank when the water suddenly became deeper, local newspaper La Provincia Pavese reported.
A family friend attempted to save the girls, the newspaper said, but was unsuccessful. A search and rescue team involving boats, divers and a helicopter was launched.
The 652km-long river flows across northern Italy, from the French border to the Adriatic Sea in the west.