The episode, which took place last week at a preschool in Laholm in western Sweden, has been reported to Sweden’s National Agency for Education (Skolverket).
The girl has made a full recovery and is back at school again, writes the Laholms Tidning newpaper.
The preschool’s permanent staff members were involved in a training course during the morning when the event occurred.
The children were accompanied by substitute teachers while out at the playground.
When it was time to go in and eat, no one noticed that the girl remained outside.
It was only when the regular teachers returned from their training about 15 minutes later that they noticed the girl was missing.
Another 15 minutes elapsed before the girl was discovered. She was lying unconscious in a concealed part of the playground.
School officials believe she most likely fell from the jungle gym and hit her head.
All preschools in Laholm plan to review their procedures as a result of the incident.
“This is a serious accident. It always raises questions about how it could have been avoided,” said Laholm municipality’s head of education Per Jangen, to the newspaper.