An eight-year-old boy crashed his parents' car and killed his sister, after the pair snuck out after bedtime to go for a joyride.
When their mother discovered they were missing, she initially feared they had been kidnapped and raised the alarm.
Spotting the woman's car driving around the US city of Phoenix, police attempted to pull it over, at which point it swerved off the road and crashed into a pole.
They found the boy – who has yet to be named – in the driver's seat suffering from an ankle injury. His sister, six-year-old Aaliyah Felder, who wasn't wearing a seatbelt and whose airbag failed to deploy, later died from her injuries.
Both were found dressed in their pajamas.
Police are currently waiting to speak to the boy, who remains in hospital.
Speaking to US TV station 3TV, local police sergeant Steve Martos said: "We want to wait. It doesn't appear that we're looking at it from a criminal standpoint."
"It was a horrible and tragic moment," he continued, as he explained how the children's mother discovered what had happened after witnessing police activity around the crash site close to their apartment complex.
From what police have managed to piece together, the two kids had managed to drive around 3 miles away from their home before turning back; apparently panicking when the police car – which was not using its sirens – attempted to pull them over.