A drunk driver has admitted running down three children in the Perth suburb of Midvale, killing one and seriously injuring another before fleeing the scene.

Key points: Kayden McPhee was killed and another boy injured in the crash

Kayden McPhee was killed and another boy injured in the crash Driver Biju Paulose was drunk and fled the scene after hitting the boys

Driver Biju Paulose was drunk and fled the scene after hitting the boys The victim's family said they were left with a pain that never went away

Family members of 15-year-old Kayden McPhee wept in the public gallery of the Stirling Garden Magistrates Court this morning as Biju Paulose, 49, pleaded guilty to a string of charges arising from the incident.

These included manslaughter and dangerous driving causing grievous bodily harm.

Kayden was with two other boys aged 16 and 12 on July 31 last year when Paulose's BMW ploughed into them as they stood on a traffic island on Farrell Road about 6:00pm.

The car ran into the group of three boys, killing one and injuring another. ( ABC News )

He died later in hospital, while the 16-year-old boy suffered life-threatening injuries.

The 12-year-old was not harmed.

Paulose also pleaded guilty to charges of driving under the influence of alcohol, failing to provide assistance to the victims and failing to report the incident to police.

Biju Paulose admitted ploughing into the children in his BMW. ( ABC News: Joanna Menagh )

'We wouldn't wish this upon anyone'

Outside the court, Kayden's family members called for a harsh sentence for Paulose, saying their lives had been changed forever.

"He was drunk, he mounted the median strip, he not only hit our grandson, he hit two boys and we have got the sentence, not him," Kayden's grandmother, Rhonda McPhee, said.

The teenager's aunt, Lee-anne McPhee, agreed.

"The pain and the sorrow that this man has caused our family is heartbreaking. We wouldn't wish this upon anyone," she said.

"He doesn't realise what he's done to us — it [the pain] never goes away."

Rhonda and Lee-anne McPhee say their lives have been changed forever. ( ABC News )

Lee-anne McPhee said her father and Kayden's grandfather, Eddy McPhee, received a call from his grandson asking to be picked up just before the crash happened.

"Dad went to pick him up, he rounded the corner and saw Kayden dying on the road. That scene will live with my father forever," she said.

She said it was also devastating that Paulose fled the scene after the crash.

"He left Kayden and that [other] boy on the side of the road like a dog," she said.

"He didn't stop and render assistance whatsoever. My nephew did not deserve that."

Paulose had his bail renewed until he faces a sentencing hearing in the Supreme Court in July.