Father’s horror after planned picnic ends with son dead, two siblings fighting for life in Blue Mountains tragedy

A father who went to work believing his wife was taking their three children on a picnic instead received the news no parent expects.

The father of the Kenyan family was at work on Sunday when he received a call telling him one of his children was dead , while his two other children and wife were fighting for life.

WATCH THE VIDEO ABOVE: Mother could be charged over Blue Mountains child stabbing tragedy

Police allege the 42-year-old mother had driven the children to a quiet street in the Blue Mountains, where she stabbed them before turning the knife on herself about 1pm on Sunday.

The children — aged five, three and one — were strapped into their car seats when the alleged attack unfolded in Valley Heights.

7NEWS understands a cyclist came across the vehicle with its doors open and found the woman bleeding.

Members of the public rushed to help, providing first aid to the woman and children while contacting emergency services.

They and their mother were treated by paramedics before being rushed to The Children’s Hospital at Westmead and Westmead Hospital in critical conditions.

Police confirmed on Monday that the woman’s injuries were believed to be self-inflicted and identified her as the suspect in the alleged attack on the children.

The woman and two surviving children remained in critical conditions on Monday.

Police said if the mother recovers from her injuries, detectives intend to speak with her with a view to laying a homicide charge.

The children’s father rushed to hospital to be with his two surviving children after being informed of the tragedy on Sunday.

7NEWS understands members of Sydney’s Kenyan community are rallying around the father, while the Kenyan consulate has also confirmed it is providing assistance.

NSW Police Deputy Commissioner Peter McKenna described the scene confronting officers as “barbaric”.