Major Crash detectives are investigating the deaths of two boys in separate incidents on the state's regional roads on Tuesday.
In the first incident, police said three boys were crossing Loch Street in Derby at about 12.50pm when one of them was hit by a white Toyota Prado.
The victim, only four years old, died at the scene.
A 43-year-old woman driving the Prado was uninjured in the incident.
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The second incident occurred about 8pm on Tuesday in the Geraldton suburb of Wonthella when a blue-and-white Honda CBR motorcycle travelling north along North West Coastal Highway collided with a green Jeep Cherokee as it turned into Eighth Street.
A 14-year-old boy from nearby Spalding, riding pillion, was critically injured and died shortly afterwards at Geraldton Hospital.
The rider, a 17-year-old boy from Geraldton, remains in a serious condition at the hospital.
The 22-year-old man driving the Cherokee was uninjured.
Police want to speak to anyone who may have seen the crashes, or the people or vehicles involved beforehand. Call Crime Stoppers on 1800 333 000 or make a report online at www.crimestopperswa.com.au.