Faulty lock in fatal fall

Boy, 5, was trapped

A 5-year-old Queens boy who fatally tumbled from a window Sunday had been trying to get out of the room through the door — but couldn’t because its lock was installed backward, cops said Monday.

An NYPD source said the little boy, William Chen, shimmied out the thirdfloor bathroom window of his family’s Corona home because he had been trapped and it was “impossible for him to get out.”

William ended up slipping and falling around 2:45 p.m., landing near the bottom of the home’s outside basement stairs, where a neighbor found his body a short time later.

“It’s unbelievable,” said another neighbor, Terry Sun, adding that the window “should have been locked” or at least had a metal guard on it. “The boy played in my home sometimes. He was very happy.”

Chen’s grandparents, who were on the second floor at the time, ran downstairs and rushed the child to NewYork Presbyterian Hospital Queens, where he died.

The boy’s parents, who own the home, had left the child in the care of his grandparents while they were running errands, police said.

Sun said he can’t imagine the guilt the grandparents must feel that the boy died on their watch.

“They loved their grandkids very much,” he said. “This is very sad.”

The condo, at 35-59 99th St., is one of four two-family units. It was being renovated at the time of the tragedy.

Neighbors said the family had been living nearby on 111th Street during the renovations and looking forward to living in their new house.

Nina Sun, Terry Sun’s wife, said the family came from China about eight years ago and she often baby-sat William.

“He was a very good boy,” she said. “They are a very nice family.”

She said the boy lived with his parents, his grandparents and another sibling.

“Six of them lived in the apartment for five years’’ before they temporarily left for the renovations, she said.

The medical examiner is performing an autopsy on William to determine the official cause of death, police said.