Local media reported the victims were killed by their mother before she tried to take her own life.
According to police in the southern Japanese prefecture of Fukuoka, a 10-year-old boy, two six-year-old girls, and a three-year-old girl were found dead early Monday.
‘Their father found them dead and reported it to police,’ a police spokesman told AFP, without providing further details.
Police are questioning the children's 41-year-old mother as a suspect in a possible murder-suicide attempt, according to Jiji Press and public broadcaster NHK.
The mother confessed to police she had killed the children, according to TV Asahi.
Police reportedly told media that at least one child had a mark indicating strangulation.
The mother was sent to hospital as her wrist was bleeding, the Asahi Shimbun daily said. She told police she cut herself with a kitchen knife but her injury was mild.
Murder-suicide cases are not uncommon in Japan and usually involve a mother killing her child or children.
Some parent-child murder-suicides have been attributed to poverty. In 2014, a single mother in Chiba prefecture killed her teenage daughter and tried to kill herself apparently because she could no longer afford to pay the rent.
On Monday, a mother and her two sons aged six and one, went missing in Gunma prefecture, northwest of Tokyo, and her car was found near a river.
Police suspect that the mother and her sons jumped into the river in a murder-suicide, the Sankei Shimbun daily reported.
Last month, a mother in Chiba prefecture killed herself after stabbing her three children, according to local media. Her 10-year-old daughter and eight-year-old son were confirmed dead.
