Police in Chongqing said they could not file criminal charges in a case in which a toddler was brutally attacked by a girl in an elevator, because the girl is only 10 years old.

The girl lives in the Xinjiang Uygur autonomous region with her mother, who was transferred there for work and took the girl with her on Monday, police said.

The 18-month-old toddler, Li Xinyuan, remained in the intensive care unit at Chongqing Medical University Children's Hospital on Friday, awaiting his first surgical operation next week to deal with his injuries.

"He would cry out when he woke up. He was in stable condition but did not make big progress," Li Shuyong, the boy's father, said on Friday as he relayed information from the child's doctor.

The father could only see his son when the boy was transferred from the ICU for checkups.

Local police neither detained the girl nor filed their investigative findings with prosecutors - which, in a case involving an older assailant would mark the start of a criminal prosecution. In this case, the attacker's young age shields her from criminal charges, the police said.

Dan Xingming, a lawyer for the toddler's family, said the local court accepted the family's civil case on Wednesday. The parents demand 300,000 yuan ($49,300) in compensation from the girl's family.

A total of 78,000 yuan had been paid as of Friday. Dan is asking the court to freeze the assets of the girl's family.

Li, the toddler's father, said the hospital costs at least 4,000 yuan a day, and the family cannot afford to pay. Both Li and his wife are migrant workers in downtown Chongqing.

Calls to the girl's father were not answered or returned.

The local education bureau in Changshou district, where the incident occurred, will conduct a review of how children's mental health issues are handled, according to the local publicity office. But no detailed information is available at this time, according to Wang Jing, spokesman for Changshou district's publicity office.

The sequence of events provided by the police shows that the 10-year-old girl, surnamed Li, went home from school at 4:10 pm on Nov 25, the same time that Li Xinyuan's grandmother took the boy for a walk.

They met at the elevator of their residential building. The girl entered the elevator as the grandmother was pulling out a baby stroller. The boy remained inside.

When the grandmother turned back to take the boy, the elevator door was closing and the girl was picking him up.

Footage from a security camera shows the girl attacking the boy repeatedly on the ride from the first to the 25th floor of the building, where she lives with her parents.

Police also released the girl's statement. She told investigators that she took the boy home and beat him on the sofa in the living room. Then she took him to the balcony to play, but the boy fell over the rail.

According to the police, the grandmother, surnamed Wu, saw the elevator stop on the 25th floor and hurried to retrieve her grandson. She met the girl walking out of the apartment and asked where the boy was. The girl lied that he had been taken by someone else, according to the police.

The girl then rode the elevator with Wu, pretending to search.

The pair separated when they reached the first floor, but the girl went straight to the bush where the boy had fallen and moved him to a spot 7 or 8 meters away.

She then went home, while Wu went to the community security office asking for surveillance footage.

The case has aroused public concerns. Song Yanhui, a faculty member at the China Youth University for Political Sciences who specializes in adolescent violence, said that she was shocked when she read the news about the attack.

But she said it was too early to analyze the girl's mental condition and motivation because information is limited.