SAN FRANCISCO, California (CNN) -- Police, U.S. Coast Guard and firefighters searched the chilly waters of San Francisco Bay and its shoreline Thursday after a mother allegedly threw her three children off a pier.Search teams found the body of one of the children late Wednesday, about five hours after police got a 911 call. Rescuers have been scouring the area since the call from a man who said he saw a woman put children in the water, San Francisco Police Chief Heather Fong told reporters Thursday. (Watch video of the search efforts -- 1:39)Officers responded quickly to the 911 call, which came in at 5:27 p.m. Wednesday (8:27 p.m. ET), and detained a woman they found walking on the pier with a stroller, according to Fong.Fong identified the woman as 23-year-old Lashaun Harris of Oakland, the children's mother.Harris has been booked on suspicion of three counts of murder, Fong said. She's in jail under the custody of the San Francisco Sheriff's Department. The chief identified the children as Treyshun Harris, 6; Taronta Greely, 2 1/2; and Joshoa Greely, 16 months.Fong asked that anyone who may have seen a woman with children and a stroller in the area contact police. Taronta Greely's body was recovered Wednesday night, according to San Francisco Mayor Gavin Newsom. The body was found two miles away from the pier. It's unlikely that anyone could survive in the 55-degree water for more than about 2 1/2 hours, said Capt. David Swatland of the Coast Guard.Authorities told the San Francisco Chronicle that Harris told them that voices told her to throw the children in the water.Relatives said Harris suffers from schizophrenia and wasn't taking her medication."She was out of her mind. She wasn't in her right mind," a woman who identified herself as Harris' cousin told KGO-TV. "Lashaun wasn't the kind of person to do anything wrong to her kids."Family members said Harris had been living at a shelter in Oakland but recently said she was going to San Francisco.Mary Ann Ramirez, the shelter's social services manager, told the Chronicle that Treyshun was "such a sweet child -- he loved school. He started first grade when he came to the Salvation Army; it was a new school." "He would come home every day, ask his mom to please take me to homework club. He really loved school. He loved his brothers, helped his mom with the kids a lot,'' Ramirez said. At a news conference Thursday, Newsom said the alleged actions make "you frankly sick to your stomach." He cited the city's resources for people who feel they can't care for their children, such as drop-off stations known as "safe havens."Scenic Pier 7, which juts some 900 feet out into San Francisco Bay and sits adjacent to the historic Ferry Building, would typically be crowded with commuters and tourists at the time of the incident.CNN's Rahul Bali, Rusty Dornin and Augie Martin contributed to this report.