The family of a 5-year-old who drowned in a river in Ehime Prefecture during a kindergarten excursion last year will sue the operator of the school, sources said Thursday.

In a suit to be brought before the Matsuyama District Court as early as July 19, the family of Shinnosuke Yoshikawa will argue that the Rosario Educational Institution, which runs Saijo St. Maria kindergarten, caused his death by allowing him to play in an area where even adults could get injured and without a safety plan in place.

The boy drowned at around 3:30 p.m. on July 20, 2012, as he, 30 other students and eight teachers played in the Kamo River in the city of Saijo. The river, which is usually about 20 to 30 cm deep, reportedly became about a meter deep in about two minutes while they were in it.

The local kindergarten did not have its legally required safety plan in place and the teachers failed to bring along a life preserver or life jackets, according to the prefectural police.

The family filed a criminal complaint in March, and the police are poised to hand their case against the institution's former president and the teachers over to prosecutors on a charge of professional negligence resulting in death.