KEWASKUM, Wis. (CBS 58) -- The Washington County Sheriff's Office is investigating after a 4-year-old child was left unattended on a school bus Wednesday, Sept. 2. 

According to the sheriff's office, the Kewaskum Police Department received a call from the child's mother just after 5:45 p.m., after the child did not arrive home. 

An officer responded to the Johnson School Bus Service facility, located just outside of Kewaskum, and located the child inside the closed bus in the lot at approximately 6:18 p.m. Officials say the child was visibly hot and partially clothed. 

It was determined the bus had been parked at approximately 5:30 p.m., and internal temperatures reached an excess of 100 degrees. 

Thankfully, the child was not injured and the parents declined emergency medical services.

According to the sheriff's office, Johnson School Bus Service, who fully cooperated with the investigation, has a standard safety protocol requiring buses to be checked at the completion of each route.

As part of the investigation, deputies learned the bus driver had previously reported a malfunction involving the bus’s electronic child reminder alarm system which is designed to audibly alert the driver after the bus is turned off to remind the driver to check the bus for any remaining students on board. The system requires the driver to walk to the rear of the bus and manually disengage the system and provides an additional opportunity to check the entire bus for children. Johnson Bus Service had ordered replacement parts for the alarm prior to this incident, per the sheriff's office. 

During the investigation, the 69-year-old driver admitted that he did not conduct a manual check of the bus after completing the route, despite the malfunctioning alarm system.

The investigation indicates that the child likely fell asleep during the bus route and was unintentionally left on the bus. 

No evidence of foul play has been suspected, but due to the child's age, the length of time remained unsupervised, the extreme temperatures inside the bus, and the driver's failure to conduct a check of the bus, the sheriff's office will refer a child neglect charge to the district attorney's office for review. 

The driver, a 69-year-old male with nearly five years of experience as a school bus driver with Johnson Bus Service, was not taken into custody.

"The Washington County Sheriff’s Office, the Kewaskum School District and Johnson School Bus Service recognize the seriousness of this incident and the concern it may cause parents and members of the community. School bus safety depends on drivers following established procedures, including physically checking the entire bus at the completion of every route, regardless of whether an automated warning system is functioning."