(CNN) To lose a brother or sister while growing up is painful enough. When it's the result of gun violence, the weight can seem insurmountable.
It's a burden often overlooked with every new headline about bullets killing children.
Kathryn "KC" Conway knows the pain these surviving siblings carry. For two decades, she's worked with the Center for Grief Recovery, a Chicago-based nonprofit that began by focusing on sibling loss.
When a child loses a sibling in an instant, Conway says, the trauma can arrest development, emotionally or physically. It can also complicate or delay grief.
The experience is different than losing a sibling to terminal illness.
When a child is sick, a family has time to process what's happening and is better equipped to grieve together when that child is gone. There's a force that brings everyone together. Family members rally around the one who is dying, and even children can participate by making cards or drawing pictures to express their love.
But when a sibling dies suddenly, there's helplessness, regret (perhaps the last words expressed during a fight that day were, "I hate you," because that's what kids do), and oftentimes survivor's guilt.
"Kids are always convinced the wrong child died," Conway says.
How parents respond to such loss can shape the surviving siblings.
"Often they become orphans at the same time because they lose parents to grief," Conway says.
Parents may not want to speak of the loss or may not know how to process it with surviving children. And that means children can flounder and feel invisible.
"How can you be special in that environment? How can you possibly make people aware of your needs, because your needs seem so trivial?" Conway says.
Siblings may believe their lives will be cut short, too, that they won't live beyond the age that their brother or sister died. When they lose a sibling in a headline-grabbing way, such as a mass shooting, they may be re-traumatized each time that story resurfaces -- or another one like it occurs.
During rights of passage -- such as graduations, proms, even getting a driver's license -- siblings often think of the one they lost, and the milestones he or she missed. Later in life, if they have their own children, the loss may be felt anew when their kids reach the final age of the brother or sister who died.
"The concentric circles of pain keep widening," Conway says. "They get less acute, less sharp, but they never become small."
The context of the gun violence -- whether it was an accident or intentional -- can also shape the coming years for surviving children, Conway says.
"It's always harder to heal from an act of human evil," she says of intentional shootings.
The nonprofit where Conway works opened in 1985 as the Rothman-Cole Center for Sibling Loss. The first of its kind, the center was the brainchild of two men who'd lost siblings early in their own lives.
For families reeling from such a loss, Conway offers some advice:
Conway marvels at those who emerge from these tragedies determined to make a difference. A child who lost a brother to gun violence, for example, could easily grow up to seek vengeance.
But there's a real power to saying, "It stops with me," Conway says. "I will do what I can to make sure no one else suffers from this. ... That's how the world heals."