He was discovered in Wharton Recreation Ground off Ledward Street, Winsford, Cheshire, at around 6.11pm on Friday, with serious injuries.
It is believed the youngster fell from playground “apparatus”, police said.
He was treated by paramedics but died at the scene.
Officers said his family have been made aware and are appealing for further information.
Detective Sergeant John Rhodes, of the protecting vulnerable people investigations unit at Cheshire Police, said: “This was a deeply tragic incident involving a very young victim and our thoughts remain with the family and friends of the boy who sadly died at the scene.
“As part of our investigation into this incident, we are asking anyone who may have been in or around the Wharton Recreation Ground area just off Ledward Street in Winsford at around the time of the incident and saw anything that may aid us in our enquiries, to please get in touch.
“At this stage I would also like to ask the public not to feed into any speculation, particularly on social media, as this remains an ongoing investigation.”
Information can be provided to Cheshire Police through the force’s website or by calling 101, quoting IML-216564.
