LOWELL — For months, neighbors watched the couple on the front porch of the light blue house, cuddling and playing with their newborn boy.

On Sunday, those neighbors agreed: These were not the kind of parents to forget a child in a car’s back seat.

“They were both good parents, and their life revolved around their kids,” said Charlotte Shuebruk, 65, who lives across the street. “It’s a sad situation that’s never going to leave them.”

Authorities are investigating the death of a 9-month-old boy who was found Saturday afternoon left in a parked car in front of the family’s home on Huntington Street.

The baby’s father discovered the boy in the family vehicle and called 911, said Jessica Venezia Pastore, a spokeswoman for the office of Middlesex District Attorney Gerard T. Leone Jr. The child was transported to an area hospital and pronounced dead.

‘You think, ‘‘How do you forget a baby?” But they seemed like nice people who loved their children. They weren’t the type of people to neglect their kids or anything like that.’

No charges have been filed in connection with the death.

“The investigation remains ongoing, however it appears the baby was left in the vehicle accidentally,” said Pastore in an e-mail Sunday. “The death, like all child fatalities, will be reviewed by the statewide child fatality review team.”

On Sunday, family and friends left flowers, stuffed animals, cards, and trays of food on the family’s porch. Near the door was a brightly-colored stand-up baby bouncer.

Authorities have not identified the child’s parents. Some neighbors said the couple has other children but authorities provided no information about the family. A woman who answered the door Sunday declined to comment. “We just want privacy,” she said.

David Cruz, 33, another neighbor, said he and his wife saw the ambulance arrive in front of the house at about 4 p.m. Saturday. He said a woman shouted, “My baby’s upstairs!” to emergency responders. The child’s father paced back and forth in front of the house, holding his hands to his head in anguish, Cruz recalled.

“You think, ‘How do you forget a baby?’ ” Cruz said. “But they seemed like nice people who loved their children. They weren’t the type of people to neglect their kids or anything like that.”

Kids and Cars , an organization that works to raise awareness about the dangers of leaving children unattended in or near vehicles, reports that vehicular heat stroke claims the lives of children with surprising regularity. As of Aug. 7, 23 children had died of vehicular heat stroke in the United States this year, according to the organization. It has been relatively rare in Massachusetts, however: Three children died between 1990 and 2010 after they were left in a hot car.

Cayenne Isaksen, a spokeswoman for the state Department of Children and Families, said Sunday that the agency is investigating, but she had no additional information.

Sunday afternoon, Shuebruk gazed at the front of her neighbor’s house. Her eyes grew wet as she thought about what could have distracted the child’s parents to the point that they would forget their infant in the back seat. Perhaps the two parents were bringing groceries into the house, she said, and confused who was supposed to retrieve the child from the car seat.

“It’s a mistake any parent could make,” Shuebruk said. “It’s a tragic accident, and they’re never going to get over it.”