A report will be prepared for the coroner after an 11-year-old boy riding a dirt bike collided with a tree on a property near Moama in the state's south.
The boy was treated by Victoria Ambulance paramedics and flown to Royal Children's Hospital in Melbourne, where he later died, NSW Police said in a statement on Sunday morning.
"Officers from Murray River Police District have commenced inquiries into the circumstances surrounding the incident," NSW Police said. A report will be prepared for the Victorian coroner.
The death comes after a teenager was hit by a ute in Sydney's west on Saturday night.
An 18-year-old woman was taken to Nepean Hospital in a critical condition about 11.30pm in Mulgoa near Penrith.
The 23-year-old driver was taken to hospital for mandatory testing.