However, Wisconsin law requires that first-degree homicide charges initially be brought in adult court if the accused is age 10 or older.
Another girl was critically injured in the collision near Lake Hallie, around 90 miles east of Minneapolis.
According to Kowalczyk, the girl said she was holding the baby when she dropped the infant, who hit his head on a footstool. Police said she was in stable condition Monday.
Two small groups of Girl Scouts and their adult chaperones wore bright green safety vests Saturday as they walked along both sides of County Highway P, which they had adopted as a community service project.
Jayna Kelley, 9, Autum Helgeson, 10, Haylee Hickle, 10, and her mother Sara Jo Schneider, 32, were killed.
Treu and his passenger admitted to police that they had been intentionally inhaling chemicals before the accident.
China motorway toll crash: At least 15 dead in Lanzhou
The semi-trailer was registered to Li's home northeastern Liaoning province, more than 2,000km from the scene of the incdient. Deadly road accidents are common in China, where traffic regulations are often flouted or go unenforced.
On Sunday hundreds of members of the community gathered together in the rain in honor of the victims of Troop 3055 and sung Girl Scout songs during the candlelight vigil.
The youngster, who can not be identified because of her age, appeared before Chippewa County Circuit Court on Monday - an adult court - because of the severity of the allegation. The mother of one of the girls killed said she was standing near her daughter when the truck came crashing toward them. The 21-year-old driver, Colten Treu of Chippewa Falls, sped off but later surrendered. Police told Fox News, "The truck failed to stop and render aid, but instead left the scene of the crash".
Haylee's father died when she was 3, Judy Schneider told the AP, and her daughter, granddaughter and grandson moved in with her several years ago.
According to the district attorney, Treu and a friend bought an air duster and were huffing in the vehicle. 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.
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.
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