Two toddlers who survived an Arkansas car crash that took the life of their pregnant mother might have gone undiscovered for more than four days, authorities said Tuesday.

"We initially thought it might have been two days they were there," said Detective Lt. Nathan Greeley of the Ouachita County Sheriff's Department in Arkansas. "With new information they could been there for four days."

It's possible the apparent solo vehicle accident on State Highway 24 happened Thursday, the department said in an updated statement on the crash.

Local authorities first responded to the area near the accident Monday at 7:50 a.m. after they received reports on an unattended toddler walking down the road, sheriff's officials said. The 3-year-old boy had sustained cuts and scratches, but sheriff's deputies weren't initially aware of the accident.

They posted a photo of the child on social media in an effort to find his parents. Sheriff's officials soon learned his mother had been missing for a few days.

On Tuesday morning deputies went back to the scene of his discovery and found a vehicle sideways "in a deep ravine not visible from the roadway," according to the sheriff's statement.

The toddler's 1-year-old brother was found alive in the vehicle — still strapped in his child safety seat. "There were no severe injuries," Greeley said.

The mother, 25-year-old Lisa Holliman, was found outside the car, deceased, according to the sheriff's department. Deputies believe she was ejected in the crash.

The woman's father, James Holliman, told NBC News affiliate KARK that his daughter was expecting. "We just found that out at the hospital that she was pregnant," he said.

"We didn't know," Holliman said. "We lost two."

The grandfather believes the 3-year-old encountered his mother's body as he left the crash scene. "When he climbed out of that car, seeing his mother laying there dead like that, like she was, he tried to wake his momma up," he said.

Both children were checked out by doctors and determined to be in good condition, Greeley said. The 1-year-old was expected to be released from a hospital Tuesday afternoon, he said.

The biggest concern, Greeley said, was "dehydration, given the amount of time" they spent without care.

The crash was being investigated by Arkansas State Police, and Holliman's body was sent to the Arkansas State Crime Lab for an autopsy, he said.

"There's no reason to believe there was any foul play," Greeley said.

"If it had not been for the 3-year-old child being able to escape the car wreckage and finding his was back to the roadway, it could have easily been three deaths," the detective said in an earlier statement.