KABUL — In Abdul Saboor Samadi’s three-story house, Wednesday morning started just like any other.

He woke his two oldest children, Dunya, 10, and Hadis, 7, then ushered them out the door for their usual five-minute walk to school, picking up their friend Mustafa and their cousin, Sana, along the way.

When they reached the main road, Samadi recalled later, he grabbed their hands as he always did, to escort them across the busy thoroughfare where buses and cars often speed on their way past the nearby airport and toward central Kabul.

Then he felt a boom.

This is what Samadi said he will always remember about what happened next: The apple he had handed his daughter moments before falling from her hand. The way he reached for his son just in time to feel the boy’s final deep breath. How he saw his daughter’s lifeless body lying a few feet away, Mustafa dead and Sana severely wounded beside her.

“Anytime I remember, anytime I speak about it, my heart aches,” Samadi, a shopkeeper, said Thursday, surrounded by friends and family visiting for a memorial service.

The suicide blast that killed the three children targeted an armored vehicle belonging to GardaWorld, an international security company, Nasrat Rahimi, a spokesman for the Interior Ministry, confirmed. At least 12 people died in the bombing and 10 were wounded, including Sana and Samadi, whose arm and leg were hit by shrapnel. Samadi was released from the hospital to attend his children’s funerals but will need surgery.

Dunya, Hadis and Mustafa are among a growing number of children killed in Afghanistan this year.

Between Jan. 1 and Sept. 30, at least 631 children were killed and 1,830 wounded, the United Nations said in a report last month, an 11 percent increase from the same period in 2018. Over the past four years, almost 3,500 children have been killed and another 9,000 wounded.

On Thursday evening, dozens of people chatted quietly outside Samadi’s house, their cars lining the dirt road he and the children had walked the morning before. Two days earlier, some of the same family members had gathered inside the house to celebrate Hadis’s seventh birthday. Photos from the occasion show the boy beaming in a checked suit and red tie, his father’s arm wrapped around his shoulder as the two show off his gifts.

Now, inside the house, Samadi’s wife, Manizha, wept uncontrollably as her older brother, Ezhar Seddiqi, pulled her close to comfort her.

“What am I supposed to do?” she cried. “Where am I supposed to go? They’re gone.”

Seddiqi, a doctor, recalled how the children had excelled in school. Dunya, a fourth-grader, dreamed of following in his footsteps to medical school, he said. Hadis was only in second grade but already hoped to become an engineer.

“All of Afghanistan, all humans that have heard about this, they’ve had their hearts broken,” Seddiqi said.

Wednesday’s bombing shook Kabul after a relatively peaceful month here. No group has asserted responsibility for the attack.

The lull in violence had been a welcome relief for civilians after an especially deadly summer, when both the Islamic State and the Taliban launched several attacks in the capital, killing civilians going about their daily lives: commuting to work, attending a wedding or crossing through a busy traffic circle.

The Taliban stepped up its attacks as it entered the final phases of peace talks with the United States — talks that President Trump abruptly canceled after a September bombing in Kabul killed a U.S. service member.

The attack came after President Ashraf Ghani announced that he planned to release three high-profile militants in hopes the move would jump-start peace talks with the Taliban and lead to the release of two hostages, an American and Australian, who were kidnapped at gunpoint in Kabul in 2016. The three commanders belonged to the Haqqani network, a hard-line group allied with the Taliban.

One day after the bombing, a small crater in the road and some blown-out shop windows were the only remnants of the attack. But a block away in Samadi’s house, the air was thick with grief.

A relative opened the door to the children’s bedroom, pointing to the mattress where they had slept. In the stairway nearby, a plastic sheet covered a window that was shattered in the blast. Outside, Dunya and Hadis’s 2-year-old brother, Sodais, played with a plastic truck, too young to understand what had happened to his siblings.

Next door, Samadi sat in a chair in his cousin’s living room, covered with a blue velvet blanket. Dozens of men sat on the floor around him, weeping as he described the attack.

Then one raised his hands and began to recite a prayer. The room went quiet as the others lifted their hands to join him, tears streaming down their faces.