For instance, if a school employee is being stalked, the principal, custodian and front-desk staff should have a photo of the stalker and description of his or her vehicle.
Nationwide, there has been more focus in recent years on training school employees about how to react quickly in dangerous situations and how to detect subtle changes in behavior, he said.
Dorn added that in elementary school, emergency drills need to be developmentally appropriate so that they don't traumatize young children. "Something that might not frighten a high school student might terrify a third-grader," he said.
Mental health professionals say that many children will be deeply affected by the shooting because it happened in an environment familiar to them, one they perceive as safe. Children will likely learn about the shooting, even if parents think they have kept the information from them, said Kari O'Grady, a pastoral counseling professor at Loyola University Maryland.
"They're probably going to hear about it at a neighbor's house or on TV, so it's important to be open with them," she said. O'Grady said parents should explain the incident to children in simple terms.
Parents should also limit their children's exposure to news coverage of the incident, particularly television reports featuring graphic images. Very young children might think that the shootings were occurring again and again, not realizing that the footage is all of the same incident, said O'Grady, who specializes in responding to crisis and trauma.
Kelly, the Hopkins psychiatrist, warned that children might have nightmares about the attack. Very young children can struggle with differentiating between reality and dreams, and need extra reassurance from parents, he said.
Children might regress — returning to sucking their thumbs or wetting the bed, for example — or they might become clingy or grow withdrawn, expert say. Parents should invite them to talk about the shooting or to express their emotions through drawing or play.
While all children will respond to the shootings differently, children who still appear disturbed about it in a week or two may need additional counseling, the experts said. They urged parents to set up an appointment with a pediatrician, mental health professional or school counselor if children remain fearful for a prolonged period.
When talking about the shooting, parents should not promise that such events could never happen to their children, but explain honestly that it is extremely unlikely, the experts said. "Children can sense when we're giving false promises," said O'Grady.
Both parents and children can take comfort in reviewing how their family would respond if there's a crisis, Kelly said. This can help children "have a sense of control in what is a fundamentally uncontrolled and sort of scary world we live in," he said.
Dr. Rahsaan Lindsey, medical director of Consultation and Crisis Intervention Associates at the Greater Baltimore Medical Center emergency room, said it's important to be open with children and willing to listen to them.
"I always stress there's nothing wrong with a little TLC, a little hug and 'I love you,' especially in situations like this," said Lindsey, a psychiatrist.
But come Monday, many children — and parents — will likely still be struggling with fears conjured up by the shooting.
"I wouldn't be surprised if there were a sudden rash of tummy aches Monday morning because kids are scared of going to school or parents are scared of dropping their kids off," Kelly said.
At least one local school system — Anne Arundel — said it plans to have county police at its schools when classes resume Monday morning.
Baltimore Sun reporter Joe Burris contributed to this article.