A father is grieving after his wife and two kids were killed in a horror crash on a major Sydney motorway.

Four-month-old baby Ivy died in hospital two days after her mother and brother were killed in a terrifying crash on a southwest Sydney motorway.

Dad Ian Prahastono was at work at the time of the accident and was reportedly alerted to the crash by his Apple Watch, according to 7News.

The Apple Watch feature detects a severe car crash and can help connect to emergency services and notify emergency contacts.

The incident happened on Monday morning when Katrina Prahastono, 34, attempted to do a U-turn from an emergency bay on the Hume Motorway and collided with a cement truck.

The car’s engine was found almost 100 metres along the road after the impact of the crash crushed the car against a guard rail, the Daily Telegraph reports.

Three members of the Prahastono family were killed in a horror crash near Menangle Park.

Katrina Prahastono and her son Kai, two, died at the scene, while her baby was taken to The Children’s Hospital at Westmead.

The infant died in hospital on Wednesday.

New South Wales Ambulance chief superintendent Mark Gibbs said the baby’s capsule had likely initially saved her life after it was pulled from the wreckage of the car.

“It shows how child restraints work in such tragic circumstances,” he said.

The couple were married for eight years. Photo / Facebook

The 48-year-old driver of the cement truck was uninjured and was taken for mandatory blood and alcohol testing.

A statement from the family said they are “heartbroken to announce the sad passing” of a “loving daughter, mother, devoted wife, sister and friend to many”.

The baby was taken to hospital in a critical condition. She later died.

An Islamic prayer group announced the mother and son’s death to its members, asking them to keep the family in their prayers.

“With great shock and heavy hearts, we announce our beloved sister and her son have returned to their creator, after being involved in a tragic accident yesterday involving a cement truck on the freeway,” it wrote.

“She was such a beautiful soul and loved by many!

“Please keep her baby in your prayers, who’s currently in hospital in a critical condition. May Allah grant this baby a swift full recovery.”