MIAMI — Jessica Kornfeld sat down with her son and daughter after school on Friday and shared with them the unthinkable, horrific news out of Connecticut: Someone had stormed into an elementary school and killed children nearly their same age.

“They’re just babies,” her 10-year-old son said. “What could they have done?”

Kornfeld assured him the victims had done nothing wrong, and that the shootings didn’t make sense to anybody. She reminded her children that they were with her, and safe.

“But it could have been us,” her son replied.

School administrators across the nation have pledged to add police patrols, review security plans and make guidance counselors available in their districts as students return to classes today for the first time since the massacre at Sandy Hook Elementary School in Newtown, Conn.

And yet, it is pretty near impossible for parents not to be anxious and apprehensive.   

“For them, you need to pretend that you’re OK,” said Kornfeld, of Pinecrest, Fla. “But it’s scary.”

Teachers shared their concerns and braced themselves for what they would face in the classroom today.    

“It’s going to be a tough day,” said Richard Cantlupe, an American history teacher at Westglades Middle School in Parkland, Fla. “This was like our 9/11 for school teachers.”

Cantlupe said he will tell his students that his No. 1 job is to keep them safe, and that like the teachers in Connecticut, he would do anything to make sure they stay out of harm’s way. He is also beginning to teach about the Constitution and expects to take questions on the Second Amendment.

“It’s going to lead right into the controversy over gun control,” he said.

In an effort to ensure their students’ safety and calm parents’ nerves, school districts across the United States have asked police departments to increase patrols and have sent messages to parents stressing that they have safety plans in place that are regularly reviewed and rehearsed.

Some officials refused to discuss plans in detail, but it was clear that vigilance will be high this week at schools everywhere in the aftermath of one of the worst mass shootings in U.S. history: Twenty-six people were killed at Sandy Hook Elementary School, including 20 children ages 6 and 7. The gunman then shot and killed himself.

In northern Virginia around the Fairfax County Public Schools, the largest school system in the Washington area, with about 181,000 students, will provide additional police patrols and counselors.

“This is not in response to any specific threat but rather a police initiative to enhance safety and security around the schools and to help alleviate the understandably high levels of anxiety,” Superintendent Jack Dale said Sunday.  

Many schools will be holding a moment of silence today and will fly flags at half staff. In addition to their students’ physical safety, administrators are also concerned about the psychological toll the shootings could take.

Dennis Carlson, superintendent of Anoka-Hennepin School District in Minnesota, said a mental health consultant will meet with school officials today, and there will be three associates — one to work with each of the elementary, middle and high school levels. As the day goes on, officials will be on the lookout for issues that might pop up, and extra help will go where needed.

“We are concerned for everybody — our staff and student body and parents,” Carlson said. “It’s going to be a day where we are all going to be hypervigilant, I know that.”

In Tucson, Ariz., where a gunman in January 2011 killed six and wounded 12 others, including U.S. Rep. Gabrielle Giffords, the largest school district in the state increased security after Friday’s shooting. Tucson Unified School District spokeswoman Cara Rene said Sunday that the district was participating in a memorial being held at one of its schools on Sunday evening, and that Gifford’s replacement, Rep. Ron Barber, would be a featured speaker along with Superintendent John Pedicone. Barber was with Giffords at the constituent meet-and-greet and was among the wounded.

Rene said planning was under way to help teachers and students with grief and fear issues when school resumes today, and the district was working with Tucson police on security issues.

Officials with Chicago Public Schools, the nation’s third-largest school district, said the district is reiterating its existing safety and emergency-management plans to keep more than 400,000 students safe, and may deploy police or counselors to schools as needed.

“With this incident, we took it as an opportunity to remind all of our principals to review and refresh their individual emergency-management plans and remind staff of standard safety protocol,” said Chief Safety and Security Officer Jadine Chou.

Meanwhile, at home, many parents were trying their best to allay their children’s fears while coping with their own. Kornfeld said she drove her children to their elementary school over the weekend to show them that it was still safe and nothing had changed.

She said her family’s Miami suburban community is a lot like Newtown, Conn., a place where people generally feel safe being at home without the doors locked and playing outside after school.

“Why would that happen there?” she said. “It kind of rocks everything.”