06/11/2012 02:52 EDT | Updated 08/11/2012 05:12 EDT

School grieves for young sisters killed in train-van crash in Lakeshore, Ont.

LAKESHORE, Ont. - Grief counsellors attended to young students and staff at a southwestern Ontario school Monday, after a six-year-old girl and her little sister were killed when their family minivan was struck by a train.

Wynter Williams, who was a senior kindergarten student at Belle River Public School in Lakeshore, Ont., died Sunday along with her three-year-old sister Brooklyn, who would have started school in September.

Their four-year-old brother Dryden was clinging to life in a Detroit hospital following the horrific crash at a level crossing outside the town, which is located about 30 kilometres east of Windsor.

The children's father, Andrew Williams, was in a Windsor hospital with life-threatening injuries, while the youngest child in the family, one-year-old Jasmyn, suffered minor injuries.

Counsellors were at the school Monday, offering support to staff and students.

"We try to make it very proactive in terms of what students can do to support their peers who are experiencing something as traumatic as the accident that happened," said Vicki Komar, supervisor of social work for the Greater Essex District School Board.

There are special challenges when dealing with such young children and their grief, she said.

"Often times especially the younger ones attribute things back more into their own families and their own personal experiences," said Komar.

Meanwhile, a Transportation Safety Board investigator was headed to the scene of the collision to try to find out what happened.

Authorities have said visibility was good at the crossing, which intersected a gravel road.

Chris Krepski, a spokesman for the Transportation Safety Board, said it's early in the investigation but efforts will be made to gather as much information as possible, including examining the wreckage, finding out what the weather conditions were at the time and interviewing witnesses.

"Our role is to advance safety and we do that by investigating accidents to determine what happened, why it happened and what can be done to prevent it in the future," said Krepski.

The freight train crew did everything it could to warn the van's driver before the crash Sunday morning, including sounding the train's whistle and hitting the emergency brakes, said CP Rail spokesman Kevin Hrysak.

The crossing has few safeguards except for a warning sign, provincial police said Sunday.

(CKLW, The Canadian Press)

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