The bicycle was a present two years ago for Dalerjon Shahobiddinov’s eighth birthday. He chose the model himself: It was bright orange, sprinkled with black and white dots .

“He was so happy and excited to ride it,” said the boy’s father, Djahongir Djalolov .

The bike was big and heavy. His father or his older sister would usually carry it down the three flights of stairs from their Brooklyn apartment. On a recent Saturday, Dalerjon took it out for a ride with his friends.

The ride would be his last one.

Dalerjon, 10, was hit and killed on Oct. 5 by an unlicensed driver while biking steps from his home in the Kensington neighborhood. The boy’s 14-year-old sister knows her brother is gone, but his 5-year-old sister keeps wondering when he is coming back.

“She is asking, where is he?” Mr. Djalolov said. “Is he coming already?” They tell her: “He is far away. When you grow old you will see him.”