Searchers found the bodies of Nicole Waring and her 6-year-old daughter Dakota downstream in Wardsboro Brook on Saturday. They found the body of 2½-year-old Grace downstream Sunday.
"For whatever reason, it was a deliberate action," said Vermont State Police Capt. David Covell, who stopped short of calling the river plunge a suicide.
Waring, 40, was reported missing early Saturday after she disappeared from her parents' Wardsboro house with the two girls, the state police said.
As troopers began preparing a search party, State Police Sgt. Robert McCarthy spotted Waring and a child standing on the edge of the brook, about 100 yards from the parents' home, Covell said.
Normally placid, the brook was swollen with rain and snowmelt and had a swift current. The water was about 3 feet deep Sunday, but authorities said it was deeper on Saturday.
McCarthy tried to talk to Waring, but she ignored him and walked into the water holding the child, police said.
She was standing near a rock in turbulent, waist-deep water when McCarthy reached for her, but she pushed away from the rock and eluded his grasp, plunging into the brook with Dakota in her arms before being swept away, Covell said.
"The sergeant tried to communicate with her. She didn't respond at all. He was in close enough proximity that she should've recognized his presence," Covell said.
Preliminary autopsy findings on Waring and the 6-year-old suggested they drowned, Covell said.
Waring had been despondent, but police wouldn't say why.
"I don't know particularly what issues were upsetting her, but she had been exhibiting some unusual behavior the day prior to and during the time Sgt. McCarthy located her," Covell said. He wouldn't elaborate.
She made no special preparations before leaving her parents' home on foot about 1 a.m. Saturday, he said.
Police have spoken with Waring's husband, Michael Waring, who was in Massachusetts at the time, Covell said.