Two children are dead after they were trapped in this car, which entered the the St. Clair River just south of the Sun Oil turn on the Aamjiwnaang First Nation Thursday night. (Tyler Kula/Sun Media)

Two children have died after the vehicle they were passengers in plunged into the St. Clair River near the Sun Oil curve in Sarnia Ont.

The vehicle left River Road and splashed into the frigid water around 7 p.m. Thursday.

Two of the four occupants, a 48-year-old Wallaceburg woman and her 12-year-old daughter, managed to escape the car and get back to land.

The driver's grandchildren, a 10-year-old boy and a six-year-old girl, were located in the submerged vehicle by emergency personnel. Efforts to resuscitate them were unsuccessful.

The two attended St. Elizabeth Catholic School in Wallaceburg, where the St. Clair Catholic District School Board sent pastoral care team and a chaplaincy leader Friday.

"We turn to our faith in times of inexplicable tragedy, and that's one of the messages we give the students," said director of education Paul Wubben.

"For some reason it seems even sadder when it happens at Christmas time, a family time."

Emergency responders at the scene included Sarnia police and firefighters, paramedics, Point Edward firefighters, St. Clair County divers, and marine units from the U.S. coast guard, Point Edward and St. Clair County in Michigan.

The grandmother and her 12-year-old daughter were treated and released at hospital.

River Road, also known as St. Clair Parkway, was closed from Churchill Road to Marlborough Avenue didn't reopen to traffic until Friday afternoon. The accident scene is adjacent the Aamjiwnaang First Nation but the road is owned by the City of Sarnia.

Aamjiwnaang Chief Chris Plain said the roadway can be treacherous, especially in winter months. Guardrails should be installed between the road and the river, he said.

"We've had plenty of people go into the river in their cars over the years. Most have been able to get out, but there have been tragedies like this too," Plain said.

He said he intends to meet with Mayor Mike Bradley and Sarnia-Lambton MPP Bob Bailey as soon as possible to discuss safety improvements on the St. Clair Parkway near the reserve.

"I want to address this issue and sit down with these people before something else happens," Plain said. "I hate to be reactive, not proactive, because I know it does no good for this family now.

"This is a tragic, tragic situation. I feel just terrible for the people involved."