All 20 children who died in a shooting at a school in Connecticut were aged between six and seven, according to an official list of the dead.
The state's chief medical examiner said the gunman used a rifle as his main weapon, and all the victims appeared to have been shot several times.
The gunman, named in media reports as Adam Lanza, killed his mother before driving to the school and opening fire.
Six adults, all women, were also killed before the gunman shot himself dead.
The head teacher at Sandy Hook school in Newtown, Dawn Hochsprung, is listed among the dead, along with adults Rachel DaVino, Anne Marie Murphy, Lauren Russo, Mary Sherlach and Victoria Soto.
Eight boys and 12 girls were killed - all but four of them were aged six.
The youngest, Noah Pozner, celebrated his birthday only last month.
A woman who worked at the school was the only person to be shot and survive.
Scores of people have left tributes at a memorial outside the school, and on Saturday evening hundreds attended a candlelight vigil
President Barack Obama is to visit Newtown on Sunday to meet families and speak at an interfaith vigil at the town's high school.
After the attack, he urged "meaningful action" against gun crime in the US.
"As a country we have been through this too many times," he said in an emotional White House address.
Hidden in cupboards
Lt Paul Vance of Connecticut state police said on Saturday that the gunman had forced his way into the school, contradicting earlier reports that he had been let in voluntarily.
Lt Vance said investigators had gathered "good evidence" in the search for a motive, without elaborating.
The gunman killed his mother at their home before driving to the school in her car and opening fire. Reports say the guns used in the attacks were registered to her.
There are conflicting reports about whether she had worked at the school in the past.
The killings took place in two rooms within a single section of the school, police have said. The shooting lasted just a few minutes.
As they heard the shots, teachers in other parts of the building tried to protect children by locking doors and ushering them into closets.
Library clerk Maryann Jacob described telling 18 children to crawl into a storage room, before barricading the door with a filing cabinet.
Connecticut Chief Medical Examiner H Wayne Carver said the gunman shot all the victims at the school with a semiautomatic rifle, at least some of them from close range.
Asked how many shots were fired, he replied: "I'm lucky if I can tell you how many I found."
The suspected gunman's father, Peter Lanza, said his family was "struggling to make sense of what has transpired".
"Our family is grieving along with all those who have been affected by this enormous tragedy," he said in a statement.
Dr Jeannie Pasacreta, a nurse practitioner and psychologist who has been advising parents on how to talk to their children, says neighbours have been cancelling Christmas parties and taking down decorations.
Pope Benedict XVI paid tribute to the victims and their families in his weekly address at the Vatican, saying he was "deeply saddened by Friday's senseless violence".
In a separate development, it emerged that hours before the Newtown attack, police in Oklahoma had arrested a teenager for allegedly plotting to shoot and bomb students at his school in Bartlesville.
Sammie Eaglebear Chavez, 18, is said to have tried to convince other students to help him carry out an attack. He has been jailed with a $1m (£620,000) bond and is due to appear in court on 11 January.
The attack at Newtown is the second deadliest shooting attack at a US school or university, after the Virginia Tech killings of 2007, which left 32 people dead and many injured.