Robin Wolfenden was practicing yoga on her balcony on a spring morning in Nashville when she heard the sirens -- the sound of first responders rushing to the scene of America's latest school shooting.

The next day she laid six stones -- a Jewish tradition -- for the victims at the entrance of the nearby Covenant School, where a 28-year-old former student broke in and stalked the halls, killing three staff and three young children.

"These kids are innocent children," Wolfenden told reporters, worried for her grandsons who are five and eight years old, only a few years younger than the students killed at the Covenant Presbyterian Church-affiliated elementary school on Monday.

Mass shootings are grimly frequent in the United States, and Nashville residents were in shock Tuesday after their city joined the nationwide roster of those that have experienced an armed assault on a school.

"It's just unimaginable to think that these beautiful kids are not going to come home again," Lisbeth Melgar, who brought her two children to see a growing memorial to the victims outside the school, told AFP as she gently tucked her daughter's hair behind her ear.

Melgar was among several parents who brought their young children among the stream of mourners visiting the memorial as the sun set on Tuesday, many of them in tears among the flowers, stuffed toys, and white crosses decorated with blue hearts.

Her daughter Alessandra, 11, said security had been tightened at her school Tuesday in the wake of the attack, with authorities only letting a few people at a time through the gate.

Her mother said there would be meetings this week with parents to discuss security, "because we do believe that we need to put more security in our schools."

"It definitely hits home for me today," said Stacie Wilford, a nurse at a local medical facility and mother to an eight-year-old at a nearby school.

"I live a mile and a half away so it's in your back door and it's so scary," she told AFP.

"You drop your kids off in the mornings and you don't think that you could get a call like this. It's just devastating. That just -- I can't even fathom."

Carolyn Lucas's children also attend a school just a 10-minute walk away from the scene of the shooting.

"I feel like our souls were shattered. It's unfathomable yet completely expected. You know, why wouldn't it happen to us?" she asked.

Despite the rate of gun violence in the country, Lucas said it's still easy to think it won't hit one's own community.

But, she said, "Of course it will. Gun violence sees no race or religion... it doesn't discriminate against anybody.

"We have to do better."

'Heartbreaking'

Kaylee Franzen, 22, who came with her 21-year-old friend Gabriella Massey to pay their respects, shares the same sentiment on gun violence.

"You hear about this happening all the time. And I don't think we've ever been somewhere where it's been so close and that in itself was really heartbreaking," said Franzen, a senior at the private Christian Belmont University in Nashville.

She said the shooting made the two women want to do something, even just by bringing flowers to the site of the makeshift memorial at the church property entrance, which was guarded by a police cruiser Tuesday.

"Even though this doesn't necessarily help anything, it sends a message that things need to change, and that thoughts and prayers alone aren't something that fixes or can aid the situation," she said.

That same message dominated a rally seeking more gun regulation that was held in Nashville on Tuesday. It had been planned before Monday's attack.

"It's horrifying to live in a world when we have to be afraid to educate our children," local mother Lisa Coffman told the rally.

To AFP she added: "You don't think it's going to happen in your city.

"And then when it does, you can't stop shaking."

© Agence France-Presse