A three-year-old kindergartener died after she was left behind in a hot school van in Pattani, police said on Thursday after arresting the driver.

The girl was discovered on Wednesday afternoon after her mother went to pick her up at the end of the school day at Bamrung Muslim School in Muang district of Pattani and was told the child was absent. The mother and a teacher located the driver, who led them to the locked van where they found the body.

"The girl's body was pale. She had no wounds. There was a little blood stain around her nose," said Montri Kongwatmai, commander of the Sai Buri district police. "She must have thrashed around."

The heat inside the stuffy van and a lack of air caused her death, Montri said, citing the autopsy results.

The 23-year-old driver admitted to failing to check whether all the children had got out of the vehicle in the morning. He was charged with negligence resulting in death.

Between 2012 and 2016, there were 13 cases of children abandoned inside school buses or private cars, statistics show, part of a worldwide phenomenon referred to as "Forgotten Baby Syndrome." Six of the Thai cases were fatal. The previous such death occurred in June when a five-year-old was left in a school van in Khon Kaen province.

"The problem with child deaths in school vans... is that (it) keeps happening due to the negligence of the service provider," said Adisak Plitponkarnpim, director of the the National Institute of Child and Family Development.