A California mom has been arrested for allegedly murdering her 12-year-old son — and critically injuring his brother — a decade after she was convicted of trying to drown him as a baby, according to authorities.

Sherri Renee Telnas, 45, was busted after 911 callers reported that she was acting “strangely” early Saturday as she walked the boys to a field near her home in Porterville, according to the Tulare County Sheriff’s Office.

Deputies found the boys unresponsive in a ditch, with the 12-year-old later pronounced dead at a hospital. His 7-year-old brother is in critical condition at Valley Children’s Hospital, according to officials.

Telnas was arrested at the scene and held on charges including murder and attempted murder, deputies said.

In 2009, the mom was convicted in Montana of trying to drown the same boy when he was 10 months old — and was sentenced to 20 years in the custody of the state Department of Public Health and Human Services, according to the Missoulian.

Prosecutors said she had been “in the throes of mental illness” when she submerged herself and her baby in a river, eventually taking him to a hospital where she admitted, “I tried to drown my baby,” according to the report.

She pleaded guilty to two counts of criminal endangerment and was ordered to undergo mental health treatment, according to the report.

At the time, the prosecutor said her sentence “ensures that this won’t be repeated.”

Following the drowning attempt, the older child was put in the custody of his father, Jacob Telnas, the Missoulian reported. It’s unclear how or why both boys were in her custody in California.

“We are aware of the Montana incident,” said Ashley Ritchie, a spokeswoman for the Tulare County sheriff, according to the Visalia Times-Delta. “We are working with multiple agencies to confirm the details.”

Officials have not said how the boy died pending an autopsy.