As the United States reels from yet another mass school shooting, experts warn that young children are suffering from its devastating impacts.

A total of three children, all age nine -- as well as three adults -- were killed at the Covenant School in Nashville in what President Joe Biden referred to as "sick" and "heartbreaking."

Children can respond in a wide range of ways including being numb to the event, being more angry or irritable, suffering from high anxiety and being fearful of going back to school, according to mental health experts.

"As a pediatrician, and as a father, I think it makes common sense that when kids are exposed to this sort of thing, that it would have potentially long-term consequences for them," Dr. Marc Gorelick, president and CEO of Children's Minnesota hospital, told ABC News.

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He continued, "And the research actually bears that out, that there are, in fact, significant behavioral and psychological impacts on children who either are victims of or witness to or even around events, such as this shooting in Nashville."

Doctors told ABC News what signs parents can look out for and how to best help their children cope.

Mental health impact of witnesses to a shooting

Dr. Daniel Marullo, a clinical psychologist from Children's of Alabama Hospital, told ABC News that many children develop resilience, or an ability to overcome serious hardships.

However, he says gun violence can impact a child's mental health, especially if they are witness to such an event.

"What would be considered a typical reaction could range everywhere from changes in mood, including being sad, angry, irritable, lowered frustration tolerance to having sleep problems," he said. "Certainly, a child may be more prone to having some nightmares or scary dreams, you might see changes in appetite."

Marullo said children who experience a traumatic even such as a shooting may have more trouble focusing and concentrating or are more easily distracted.