The mother and son killed in Tuesday's horror head-on crash have been named.

The victims of Tuesday’s horror collision near the NSW town of Wilton have been named.

Julie Bullock, 49, and her seven-year-old son Hudson were killed after a car crossed onto the wrong side of the Hume Highway, colliding head-on with their Mazda 4WD.

Hudson’s twin sister, Sienna, survived the crash and was rushed to Westmead Children’s hospital where she remains in a critical condition.

The Occupational Therapist and her two children were on their way to Wollondilly Anglican School this morning when the crash occurred just prior to 8am.

Witnesses rushed to their aid, performing emergency CPR on the Picton mother until emergency services arrived.

She was pronounced dead at the scene.

One bystander claimed to have been holding Hudson when the primary school student lost consciousness.

“We were trying as hard as we could to keep the little boy alive and awake but he went unconscious on us. There was nothing we could do,” the witness told The Daily Telegraph.

“There was also a nurse who just happened to be driving by and she tried her hardest."

Hudson was pronounced dead on arrival at Liverpool Hospital this morning.

The 49-year-old driver of the Holden Astra that struck them was also rushed to Liverpool Hospital, where she remains in a critical condition.

Wollondilly Anglican School headmaster Stuart Quamby paid tribute to the Bullock family.

“The kids were and are very well loved by the community and the school,” Quamby told The Daily Telegraph.

“[Hudson] was a great little kid and his sister is a terrific kid as well.

“It is going to be tough because there is will be a lot of hurt in the community, because we are a small community out here; it is a country community.”