Just days before leaving on a family vacation to Kaua'i, Lam Kim Yim was so excited she went shopping for swimming equipment at Costco near her home in Irvine, Calif.

"She didn't know what they were going to do there, but she wanted to make sure her kids had everything they needed for a good time," said Yim's neighbor Phuoc Quach.

On Thursday, Yim; her husband, Yong; and their 7-year-old son Brandon were killed when their rental car was broadsided by a Gas Company propane truck on Kaumuali'i Highway between Kekaha and Waimea, police said. The Yims' 5-year-old son Lindon was in critical condition yesterday at The Queen's Medical Center.

"I told her before she left that she should just enjoy the time with her kids," Quach said. "You never think about something like this happening. And now ... everybody in the neighborhood is just crying."

The Yims were a close-knit family living in an Irvine neighborhood of single-family homes filled with Korean, Vietnamese, Pakistani, Chinese and Mexican families who all looked out for one another, Quach said. "They watched my home when I went on vacation, and I was looking out for their home while they were gone," he said.

Lan Kim Yim, 44, was a nurse, and Yong T. Yim, 43, was an attorney. Both valued the time they could spare to spend with their boys, Quach said.

Every Sunday, they went to church in the morning and liked to go off to the park together in the afternoon, said Quach, who said he found out about the deaths when Yong Kim's brother knocked on his door Thursday evening and broke the news.

Lam Kim Yim, driving a Chevrolet Impala rental car, was headed west and had pulled onto the shoulder of the road near mile marker 24 on Kaumuali'i Highway about 10 a.m. She was attempting to make a U-turn when the car was hit by the truck, according to Kaua'i police Lt. Mark Scribner.

Emergency rescue personnel had to use a Jaws of Life machine to help free the family from the mangled vehicle, police said. The mother died at the scene, the father was pronounced dead at Kaua'i Veterans Memorial Hospital, and Brandon died en route to Honolulu for treatment. The younger son was transported to Honolulu by an air ambulance.

The driver of the Gas Company truck, Eddie Taniguchi III, was not seriously hurt in the crash.

"We're continuing to investigate the crash, but at this point there were no mechanical problems with either vehicle, Scribner said.

Autopsies yesterday determined that all three Yim family members died of massive head trauma, Scribner said. The two boys were in the back seat of vehicle, and everyone in the car was wearing a seat belt at the time of the accident, he said.

"Brandon was a very smart boy who liked to play baseball and swim," Quach said. "I can't believe he's not coming home."

Reach Mike Leidemann at mleidemann@honoluluadvertiser.com.