LOWELL, Mass -- The family of a Bellingham woman is struggling to understand why she would have tried to cross a busy highway with her nephew and niece.

All three were killed Friday night in an horrific accident on Route 495 in Lowell.

“This is a case of bad things happening to good people and you don’t know why. It’s just a horrible thing,” Candelora Coady, the woman’s mother and children’s grandmother, told the Boston Herald.

Marcelle Thibault, 39, was taking the children to her Bellingham home for a family sleepover.

Thibault was driving in the wrong direction on the highway when she drove her 2003 Lincoln on to the grassy shoulder of the road, state police said. She was traveling southbound in the northbound section of the road.

Thibault then got out of the car with 4-year-old Shane and 5-year-old Kaleigh Lambert. The three walked out into the middle of the road, police said, where they were hit by two cars.

“We wouldn’t guess what they were doing and why they were doing it,” Massachusetts state police Lt. Eric Anderson said.

All three were taken to hospitals and pronounced dead. The boy and girl are the children of Thibault's twin sister, Danielle Lambert of Brentwood, N.H.

“I know in my heart that she was doing what she thought was best,” Thibault’s sister, Stacey Coady told the newspaper. “She wasn’t a stupid person. She knows how dangerous roads are.”

The first car driven by Jennifer Jolly, 47, of Lowell, hit the three in the right or middle lane. A second car driven by James Scammon, 43, of Portsmouth, N.H., then hit them in the left lane, state police said.

"It's as bad as you could possibly ever think it could be," Lowell Fire Department Capt. Robert Beane told the Lowell Sun. "It's one of the worst scenes I've been to."

Thibault was taken first to Holy Family Hospital in Methuen and later to Massachusetts General Hospital in Boston, where she died. The two young children were taken to Lawrence General Hospital where they were both pronounced dead.

Neither Jolly nor Scammon were injured.

"I lived on the Lowell Connector for 10 years and this is the saddest scene I've been to," Beane told the newspaper.