Getting back to routines is key for children to move on, Garbarino said. If Friday is usually pizza night, have pizza. If swim practice usually happens on Saturday, take your child to swim practice at the normal time.

If children are too scared to return to school, parents should try to go with them as far as they will go, Garbarino said. If a child becomes hysterical upon arrival, take him or her back to the car and see if you can ease the fear, he said. Avoid reinforcing the fear.

"Hopefully by the time they do go back to school, I'll have done a good enough job at talking to my kids and make them feel at least the most comfortable they could," Procaccini said.

It's important for adults to get the help they need, too, Marans said, so they can be resources for the children who need them.

"It's such a convergence between our worst nightmares coming true, and there is a sense of helplessness and loss of control that we need to address," he said.

Interventions include helping parents understand the emotional consequences of an event like this and what to look for in their children.

The Child & Family Traumatic Stress Intervention program, which was developed at Yale at Marans' center, aims to increase communication between parents and children and prevent longer-term disorders.

When other risk factors are present that make recovery more difficult, there are other strategies. These include trauma-focused cognitive behavioral therapy, a specific type of psychological therapy that targets thinking and behaviors.

"With the right help, children are very resilient," Rodda said. "We have many different ways to help people who have experienced a trauma now that allow them to come out on the other side as survivors."

Based on experience, Garbarino estimates that 85% of kids would return to normal functioning, from a mental health standpoint, within a year after an event like the Connecticut shooting.

"Not to say they would have forgotten it," he said, "They may still make life choices because of it."