WEST MEMPHIS, Ark. — A 5-year-old found unresponsive on a day care van in West Memphis Monday afternoon died at the scene, reports CBS Memphis affiliate WREG-TV.

Police said the boy was picked up before 7 a.m. but didn't make it off the van.

Authorities said there were two adults on board — the driver and a monitor — but they somehow missed the boy when they were escorting the other children off the bus.

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Police believe the child, who was in a booster seat, was asleep, but they're not sure if he never woke up or was perhaps disoriented.

"He had no disabilities that prevented ... he was mobile, he was also vocal," West Memphis Police Capt. Joe Baker said.

Police said he was found around 3:30 p.m. when the staff at Ascent Children's Heath Services went to prepare the van to bring children home.

By that point, it was too late: First responders couldn't resuscitate him, says WREG.

Police pointed to the heat as the cause of death. The temperature outside was 91 degrees, and police said the inside of the van could have gotten up to 130 degrees.

Police and the Department of Human Services are both investigating possible negligence by multiple people.

Police said they haven't had issues with Ascent in the past.

But WREG uncovered that Ascent had previously been cited for the following violations:

1. Aug. 25, 2016, visit: Medicine shall be kept out of the reach of the children when dispensing and shall be stored in a locked area at all other times.

2. March 20, 2017, visit: Trampolines shall not be used. (Therapeutic use of trampolines is acceptable if supervised by the therapist on a one-on-one basis.)

3. March 20, 2017, visit: Slides shall have a transition platform of at least 14 inches deep for preschool and school age children, and 19 inches deep for toddler.