Six-year-old Arielle Pozner was in a classroom at Sandy Hook school when Adam Lanza burst into the school with his rifle and handguns. Her twin brother, Noah, was in a classroom down the hall.
Noah Pozner was killed by Lanza, along with 19 other children at the school, and six adults. Arielle and other students' siblings survived.
"That's going to be incredibly difficult to cope with," said Dr. Jamie Howard, a clinical psychologist at the Child Mind Institute in New York. "It is not something we expect her to cope with today and be OK with tomorrow."
READ: Two Adult Survivors of Connecticut School Shooting Will be Key Witnesses
As the community of Newtown, Conn., begins to bury the young victims of the Sandy Hook elementary school shooting today, the equally young siblings of those killed will only be starting to comprehend what happened to their brothers and sisters.
"Children this young do experience depression in a diagnosable way, they do experience post-traumatic stress disorder. Just because they're young, they don't escape the potential for real suffering," said Rahil Briggs, a child psychologist and professor at Montefiore Medical Center in New York City.
Arielle and other survivor siblings could develop anxiety or other emotional reactions to their siblings' death, including "associative logic," where they associate their own actions with their sibling's death, Howard said.
"This is when two things happen, and (children) infer that one thing caused the other. (Arielle) may be at risk for that type of magical thinking, and that could be where survivor's guilt comes in. She may think she did something, but of course she didn't," Howard said.
Children in families where one sibling has died sometimes struggle as their parents are overwhelmed by grief, Howard noted. When that death is traumatic, adults and children sometimes choose not to think about the person or the event to avoid pain.
Interested in How to Help Newtown Families?
"With traumatic grief, it's really important to talk about and think about the children that died, not to avoid talking and thinking about them because that interferes with grieving process, want their lives to be celebrated," Howard said.
Children may also have difficulty understanding why their deceased brother or sister is receiving so much, or so little, attention, according Briggs.
"I think one of the most challenging questions we can be faced with as parents is how to 'appropriately' remember a child that is gone. So much that can go wrong with that," Briggs said. "You have the child who is fortunate enough to escape, who thinks 'Why me? Why did my brother go?' But if you don't remember the sibling enough the child says 'it seems like we've forgotten my brother.'"
"They may even find themselves feeling jealous of all the attention the sibling seems to be receiving," Briggs said.
Parents and other adults in the family's support system need to be on alert, watching the child's behavior, she said. Children could show signs of withdrawing, or seeming spacy or in a daze. They could also seem jumpy or have difficulty concentrating in the wake of a traumatic event.
"For kids experiencing symptoms, and interfering with ability to go to school, they may be suffering from acute stress disorder, and there are good treatments," Howard said.
"The more directly affected you are by a trauma and perceive it as scary -- like you almost died -- the harder time you have. They'll associate school with the shooting. It will be challenging and they will need support, but we do want to confront the things associated with the trauma, that's how we get over it," she said.
It will be vital in the next weeks for parents of surviving siblings to return the surviving child to a normal routine, including regular meals, sleeping, and physical habits, Howard and Briggs said.
"They need to make sure she's doing well in school and able to make and keep her friends, and then move on to celebrating (Noah's) life, and trying to find a way to honor him. This is going to shift as we get further away from the actual day of this horrible thing," Howard said.
"Children may demonstrate pretty severe bouts of anxiety, or clinginess, or reluctance to go to school when it reopens, or separate from their parents," Briggs said. "They may be more irritable, are crying more often, are more difficult to soothe. You'll see other children who experience a few days of disruption but very much get back into rhythm of life, the routine of life, which is very important for parents to keep up."
Briggs and Howard both noted that parents must try to create a stable environment for the child, and make them feel safe, even if the parents are dealing with trauma, too.
"It's time to call in all the reinforcements you have. Accept all those offers of help that get dismissed so often. If there's a grandparent, aunt and uncle, or sibling to come in relieve you from your primary duties, it is far better to bring in a beloved family member than it is to crack when undergoing such stress," Briggs said.
"You don't want to lie to child and say everything's fine, but it is really overwhelming to a child if you are sobbing daily and unable to keep thehome running. That sends them a message more than anything else that something is really wrong here," Briggs said.
If a child's appetite or sleeping habits change, or if they show any regressive behaviors, including wetting the bed or trouble separating from their parents, it may time to seek professional help, experts said.
Child pscyhologists, counselors, teachers, therapists, and clergy are all specially-trained professionals who can help deal with grief, and talking about the tragedy in a calm and supportive way will help the child most, Briggs said.
"The best thing to do in general is try to keep the routines of the family as consistent as possible, and try to convey the ability to keep them safe and confident in that, so you do not seem as anxious and distraught over it as you probably are," Briggs said. "If you're seeing some of these signs, can always wait a couple of days to see how it goes, but again, this is the moment to avail yourselves of help that is out there."