The driver accused in the hit-and-run deaths of three Wisconsin Girl Scouts and one of their mothers is expected to be formally charged Tuesday morning.
Treu remains at the county jail on $250,000 bail, reports CBS News correspondent DeMarco Morgan.
A fourth girl, 10, was injured.
Police said that they received a call from a caretaker saying that they had found the boy bleeding from the head and unresponsive.
"This is a awful reminder of our nation's epidemic of self-indulging with substance abuse without regard of the consequences", Lake Hallie Police Department Chief Cal Smokowicz said in a statement. The children and their adult chaperones wore bright green safety vests as they walked along both sides of County Highway P, which they had adopted as a community service project.
The Lake Hallie Police Department says the four people killed are 9-year-old Jayna Kelley of Lake Hallie, 10-year-old Autum Helgeson, also of Lake Hallie, and 10-year-old Halee Hickle and her mother Sara Jo Schneider of Lafayette.
The youngster, who has not been named, told a court Monday that she was holding the little boy at a licenced day care center when she accidentally lost her grip on him. The woman killed was the mother of one of the girls killed, Lake Hallie Police Department said in a statement.
The unnamed girl was at her foster parents' home in Tilden when she allegedly dropped the baby boy on October 30, Chippewa County District Attorney Wade Newell said in court Monday.
Haylee also enjoyed painting and working on clay pottery with her mother. She in stable condition Monday at a hospital.
Treu faces four counts of homicide by intoxicated use of a vehicle. He surrendered to authorities Saturday.
Police say they were hit over the weekend when the pickup veered off a rural highway in Lake Hallie as they collected trash along a rural highway and then sped away.
Hundreds of community members held a candlelight vigil on late on November 4 outside Halmstad Elementary, the school the victims had attended.
Lake Hallie Police Sergeant Daniel Sokup said Mr Treu's black Ford F-150 ute crossed a lane and veered into a roadside ditch, striking the victims.