The 10-year-old is accused of then stomping on the baby's head until he stopped crying.
Treu, 21, was to appear in Chippewa County Court Monday, Oct. 5.
Officials said she had been removed from the home of her biologial parents and was placed in a foster home. Another 10-year-old girl who was struck was in stable condition at a hospital Monday.
A 10-year-old girl has appeared in court in Wisconsin charged with killing a six-month-old boy.
Colten R Treu has been arrested and confined in the Chippewa County Jail on 4 counts of Homicide by Negligent Use of a Motor Vehicle, 5 counts of Hit and Run and 4 counts of Homicide while intoxicated (use of inhalants).
Schneider said her daughter's "favorite time with her kids was all in their jammies, curled up to watch a movie".
Colten Treu, 21, sped off after the collision in Lake Hallie Saturday morning, but later surrendered.
Treu and his passenger, who also turned himself in, allegedly told police that right before the crash they "had been intentionally inhaling chemical vapors," also known as "huffing".
She was ordered held in custody on $50,000 bond until her next court appearance.
The children were all fourth graders at Halmstad Elementary School and Southview Elementary School in nearby Chippewa Falls, about 145 kilometres east of Minneapolis.
Police questioned one adult and three children who were present at the day care center.
Prosecutors claim she admitted dropping the baby, who hit his head on a footstool.
Haylee also enjoyed painting and working on clay pottery with her mother. The City of Chippewa Falls Police discovered the truck abandoned in the garage at the home, but neither the driver nor the passenger was still at the location, police said.
Sherri Jasper, a Girl Scout board member and counselor at Halmstad Elementary School, leads the program for a candlelight vigil Sunday at the school in Chippewa Falls, Wisconsin.
Lake Hallie police Sgt. Daniel Sokup says the pickup crossed a lane Saturday morning and veered into a roadside ditch, striking the victims.
Meanwhile, a GoFundMe account has been established for the families of those who lost their lives during the Girl Scout trash cleanup.