Three children were allegedly killed by their mothers in separate incidents in New York City last week — a type of murder-suicide that experts say is not uncommon.

Incidents of filicide tend to involve women who struggle with mental illness or have experienced it in the past, have suffered loss through death or divorce, or face impending custody disputes, experts say.

Cheryl Meyer, professor of psychology at Wright State University in Ohio, who co-wrote two books on maternal filicide, said that “in very many instances,” like in these two cases, mothers decide to take their own lives and, seeing their children as an extension of themselves, attempt to kill them as well.

“It fits the whole idea, ‘I can’t leave these children behind,’” said Meyer, describing what mothers who killed their children told her. “’No one can raise them like I can raise them.’”

A 5-year-old boy and his 4-month-old sister were found dead last Thursday in the Bronx after their mother, Lisette Bamenga, allegedly gave them windshield fluid, turned on the gas and slit her wrists. A day later, a 7-year-old boy in Brooklyn died after his mother, Tenika Revell, allegedly hit his head with a hammer, and then took pills to try and kill herself.

Bamenga, 29, now faces two counts of murder charges for the death of her children, Trevor Noel Jr. and Lillian Noel.

Revell, 40, is charged with murder, manslaughter and endangering the welfare of a child – her son Bernard, a law enforcement official said.

Numbers of maternal filicides are difficult to establish, because they are often classified only as homicides. Mayer said that in the 1990s there were approximately 100 cases a year nationwide, which is likely an underestimate because victims are not always found. She added that from her research, she estimated about half the women who killed their children attempted suicide, and half of those who attempted suicide were successful.

The cause of death for the three children killed last week has not yet been determined and is pending toxicology and tissue testing, according to the spokeswoman for the Medical Examiner’s office.

The Administration for Children’s Services, citing privacy rules, declined to say if the families were under its supervision.