A five-year-old boy is dead, and another boy and man seriously injured, after being hit by a car while riding their bicycles in Kununurra on Saturday. 

Police have confirmed the man, 37, is understood to be the father of the two boys, aged nine and five.

A spokeswoman said about 4.45pm, a white Toyota Landcruiser was headed west on Victoria Highway when it hit the two bikes.

One carried the oldest boy, the other the man and the youngest boy as pillion passenger. 

The five-year-old died at the scene.

The others were taken first to Kununurra District Hospital then flown by the Royal Flying Doctor Service to the Royal Darwin Hospital for further treatment.

The father was in surgery on Sunday morning while the nine-year-old boy was in a stable condition, a spokeswoman of the Royal Darwin Hospital said.

The 56-year-old driver of the 4WD was uninjured.

Police need to speak to anyone who saw the crash, or the Toyota Landcruiser or cyclists beforehand. 

Call Crime Stoppers on 1800 333 000 or make a report online at www.crimestopperswa.com.au.

The incident came just over a week after a 12-year-old boy died in hospital, having been hit by a truck while riding his bike in Butler.