LOS ANGELES — His 5-year-old sister keeps asking when Marine Cpl. Carlos Pineda will come home. Although more than a 100 people packed into his funeral, she insists the man in the wooden box was a doll, not her brother.

“What do I say to her?” asked Pineda’s mother, Silvia Hernandez, on Thursday from her home in Los Angeles. Hernandez buried her oldest son last week after the Camp Lejeune, N.C.-based Marine was killed during combat in Fallujah, Iraq.

“I can tell her that he died doing what he believed in, but the pain is the same,” she said.

Pineda, 23, died July 1, as a result of wounds from enemy small-arms fire. He was assigned to 8th Marine Regiment, 2nd Marine Division, II Marine Expeditionary Force.

Pineda, a native of El Salvador, grew up fast in East Los Angeles. His father was murdered by local gang members when Pineda was 9, and he quickly became the man of...