On a rain-soaked block in Kensington, Philadelphia’s acting police commissioner, Christine Coulter, struggled Sunday to understand the second grievous shooting of a child in less than 24 hours.

“No child should be murdered in their living room. It’s just terrible,” Coulter said at the corner of Ontario and Water Streets. “The wanton gun violence, the disregard for people’s lives or safety. To shoot into an occupied house is something I can’t comprehend.”

A 2-year-old girl was killed on that block about 3:30 p.m. Sunday, when an unidentified gunman fired a rifle into her family’s home, according to Coulter. The child was shot once in the back of the head, and pronounced dead at the scene minutes later.

The girl, who was not identified by investigators, was the 278th person to be killed in Philadelphia this year. Her death closely followed a shooting in Hunting Park on Saturday night, when an 11-month-old boy was struck four times. The baby remained in critical condition Sunday, according to investigators.

The shooting in Kensington also wounded the child’s 24-year-old mother, who was shot in the head and back, and a 33-year-old contractor, shot once in the stomach as he was performing work on the house, police said.

Both were taken to Temple University Hospital, where the man was in critical condition and the woman in stable condition late Sunday, police said.

Coulter said it was too early to determine the motive in the shooting, but she was confident that the house was targeted by the gunman, who fired seven shots through its front windows and door.

“It’s heartbreaking,” she said. “Any crime, anybody shot is a horrible thing, but when people indiscriminately shoot and kill babies — it’s unexplainable. I can’t imagine.”

Police officials spent most of Sunday night on the block, collecting surveillance footage from nearby businesses. They also were investigating a separate shooting that occurred about five minutes before the fatal gunfire seven blocks away, on Clearfield Street near C Street, Coulter said.

It was unclear if the two cases were related.

Earlier Sunday, the Philadelphia Fraternal Order of Police posted a $5,000 reward for information in connection with the 11-month-old’s shooting in North Philadelphia.

The baby was shot four times — once in the back of the head and the chest, and twice in the buttocks — while in the back seat of a car driven by his stepmother on the 700 block of West Luzerne Street in the city’s Hunting Park section about 7:51 p.m. The woman did not realize that the baby had been shot until she got to her home in Logan, police said.

City Managing Director Brian Abernathy, speaking next to Coulter in Kensington early Sunday evening, vented his frustration at the recent spike in violence.

“At what point do we as a city say enough is enough?” he asked. “We’ve had two kids shot in such a short period of time. They certainly didn’t deserve this, their families didn’t deserve this, our communities don’t deserve it.”

Staff writers Sam Wood and Diane Mastrull contributed to this article.