Prime minister Prayuth Chan-ocha visited the scene in Uthai Sawan - a town 500km northeast of Bangkok - on Friday to meet with bereaved families, while king Maha Vajiralongkorn is due to visit.
Most of the youngsters who died at the Young Children’s Development Center on Thursday were stabbed to death, police have said.
Children as young as two are among the 23 dead, as the tragedy marks one of the worst child death tolls in a massacre by a single killer in recent history.
Grief-stricken loved ones were on Friday seen gathered outside the nursery, with some parents clutching children’s blankets and toys.
Seksan Sriraj, 28, whose pregnant wife due to give birth this month was killed in the attack, said: “I cried until I had no more tears coming out of my eyes. They are running through my heart.
“My wife and my child have gone to a peaceful place. I am alive and will have to live.”
Royal and government representatives in white uniforms laid wreaths at ceremonial tables in front of the centre’s main door on Friday morning. They were followed by weeping family members, who gathered their hands in prayer before laying white flowers.
Photos taken by first responders in the aftermath of the tragedy on Thursday showed the nursery’s floor strewn with the tiny bodies of children still on their mats, where they had been taking an afternoon nap. Abandoned juice cartons were scattered across the floor, while alphabet pictures and colourful decorations adorned the walls.
“It’s a scene that nobody wants to see,” said Piyalak Kingkaew, an emergency worker heading the first responder team. “From the first step when I went in, it felt harrowing.
“We’ve been through it before, but this incident is most harrowing because they are little kids.”
Police have identified the killer as Panya Khamrab - a former member of the force who was discharged over drug allegations, and who was facing trial on a drugs charge.
Following the attack, he went home and shot dead his wife and child before taking his own life.
The former policeman had appeared in court earlier in the day, before going to the daycare centre to collect his child, police spokesperson Paisal Luesomboon told broadcaster ThaiPBS.
He began the killing spree after finding his child was not there, said Paisal, adding: “He started shooting, slashing, killing children.”
One teacher told public broadcaster Thai PBS that the assailant got out of a car and immediately shot a man eating lunch outside, then fired more shots. When the attacker paused to reload, the teacher had an opportunity to run inside.
“I ran to the back, the children were asleep,” said the young woman, who did not give her name, choking back her words. “The children were two or three years old.”
Another witness said staff had locked the door to the room where children were sleeping, but the gunman shot his way in.
“The teacher who died, she had a child in her arms,” the witness, whose name wasn’t given, told Thailand’s Kom Chad Luek television. “I didn’t think he would kill children, but he shot at the door and shot right through it.”
“He was heading towards me and I begged him for mercy, I didn’t know what to do,” another distraught woman told Thai PBS, fighting back tears.
The killer’s mother told Nation TV “I don’t know [why he did this], but he was under a lot of pressure,” citing debt the former policeman had clocked up and his drug taking.
About 30 children were at the facility - a pink, one-storey building surrounded by a lawn and small palm trees - when the attacker arrived. That was fewer than usual, as heavy rain had kept many people away, said district official Jidapa Boonsom.
Police said three boys and a girl who survived the attack were being treated in hospital.
UK prime minister Liz Truss is among global leaders who have sent sympathies to the families of the victims, tweeting that she was “shocked to hear of the horrific events in Thailand”.
“My thoughts are with all those affected and the first responders. The UK stands with the Thai people at this terrible time,” she added.
The massacre is among the worst involving children killed by one person.
Anders Breivik killed 69 people, mostly teenagers, at a summer camp in Norway in 2011, while the death toll in other cases include 20 children at Sandy Hook Elementary School in Newtown Connecticut in 2012, 16 at Dunblane in Scotland in 1996 and 19 at a school in Uvalde, Texas, this year.
Gun laws are strict in Thailand, but ownership is high compared with some other countries in Southeast Asia. Illegal weapons, many brought in from strife-torn neighbouring countries, are common.