The White Oak teen accused of killing his infant sister will be tried as a juvenile on a lesser charge than originally brought against him, a judge ruled Friday.

Montgomery County District Court Administrative Judge Eugene Wolfe agreed to drop a first-degree murder charge against the 14-year-old boy in favor of a second-degree charge. Because of the boy’s age, the new charge means he will not be tried as an adult.

The boy was charged in the suffocation death of his 7-month-old sister, Larissa Yanes, after rescue workers found her unresponsive in the family’s apartment in the White Oak section of Silver Spring.

According to charging documents, the 14-year-old allegedly struck his sister and covered her mouth with his hands to make her stop crying. When she finally stopped making noise, he allegedly walked her around the family’s apartment and then placed her in a car seat, according to the documents.

Gloria Yanes, the children’s mother, left her son with the baby on Feb. 7, when she went to work a night shift as a cleaner. She told police that the boy had watched Larissa without incident many times before. She had asked him if he wanted her to leave Larissa with a friend so he could get more sleep, but he declined, she said.

Another child, a 3-year-old girl, also was home at the time.

When Yanes returned home at 5:30 a.m. on Feb. 8, she thought Larissa was sleeping and did not try to wake her until around 6 a.m. to feed her. That’s when she realized Larissa was unresponsive and called 911.

The rescue team took the girl to Holy Cross Hospital in Silver Spring, where she died from her injuries.

The cause of death was asphyxiation, State’s Attorney John McCarthy said.

One reason for the switch to a lesser charge was the fact that most of the visible injuries resulted from “postmortem insect activity,” McCarthy said.

The boy did not attend the hearing but his mother did, with a handful of friends, including the priest who had officiated at her daughter’s funeral.

She has not seen her son since he was arrested, she said in Spanish, adding that she had hoped to be able to see him and speak with him at the hearing.

“I was hoping to see him and see the expression on his face,” she said.

She described her son as a joker with a playful personality.

He had come to the United States in 2010, she said, a few years after she arrived in November 2006. He adapted rapidly to American culture, she said, and although he had struggled in school, his grades had recently started to improve.

If he had been at the hearing, she said, “I had the hope that he would speak and say it wasn’t him.”

The suspect, an eighth-grader at Francis Scott Key Middle School, is being held at Alfred D. Noyes Children’s Center. The Washington Post generally does not identify juvenile suspects.

If convicted, the teen’s punishment will be up to a judge’s discretion, according to McCarthy.