A mother's attempt to save her two young children ended tragically Tuesday after officials said fast-moving water swept the siblings down a stream in the San Bernardino Mountains in California.

The San Bernardino County Sheriff's Office reported at 1:45 p.m., a woman took her 2-year-old son and 4-year-old daughter to spend the afternoon at the Thurmun Flats Picnic Area, which sits above the banks of Mill Creek, a major tributary of the Santa Ana River.

"The mother and her children were playing near the river with rapid water moving downstream," the sheriff's office wrote in a news release.

Just after 3 p.m., deputies reported, the mother was attending to her son when her daughter was swept downstream. The woman searched for her daughter but could not find her and, when she returned to her son, he was also missing and also assumed to be down river.

"After frantically searching, she hiked up to the picnic area and contacted another family to help search for the children but were unsuccessful in locating them," the release continues.

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Children both found at river's edge

Just after 4 p.m., deputies from the Yucaipa Station, the sheriff’s Air Rescue team, Mentone Station County Fire personnel, and the U.S. Forest Service crews began assisting in the search for the missing children.

At approximately 4:39 p.m., crews located the 2-year-old boy near the edge of the river, and shortly after 5 p.m., found the 4-year-old girl also at the river's edge, the sheriff's office reported.

First responders transported the siblings to local hospitals, the release continues, where "after extensive life saving measures," the children were pronounced dead.

Victims' identities pending

The San Bernardino County coroner's office will determine the children's exact cause and manner of death.

As of Wednesday, the office had not released the victims' names or said where they are from.

Anyone who witnessed the incident is being asked to contact the sheriff's office.

Natalie Neysa Alund is a senior reporter for USA TODAY. Reach her at [email protected] and follow her on X @nataliealund.