The suspect then attempted suicide by throwing herself under a train, before being rescued with serious but not life threatening injuries, said lead investigator Marcel Maierhofer.
She is believed to have “carried out the act while she was feeling emotionally overwhelmed, and that too is the motive,” said the investigator.
Police believe that the three girls aged one, two and three, and two boys aged six and eight were sedated and then smothered to death either on Wednesday or Thursday.
A sixth child, 11, survived. He had told schoolmates in a group chat that all his siblings were dead, said investigators.
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He was likely able to avoid the grim fate of his siblings because he was in school at the time of their killing, said Maierhofer.
Police found the bodies in the suspect's apartment in the city of Solingen near Düsseldorf in the state of North Rhine-Westphalia after they were alerted by the suspect's mother, who had herself learnt of her grandchildren's fate from her daughter.
The suspect is believed to be emotionally distressed after a separation from her third husband a year ago.
The man is the father of four of the six children.