The 70-year-old monarch went to a hospital in Nong Bua Lamphu on Friday evening where the wounded from one of the worst attacks in the kingdom are being treated, 36 dead including 24 children.
On Saturday, families and loved ones gathered in a Buddhist temple, marking the start of three days of funeral rituals.
The incense mingles with the smell of the countless bouquets of flowers arranged around the coffins, many of which are topped with photos of the smiling, chubby faces of the children shot dead by Panya Khamrab, an ex-policeman.
Flowers and toys given as gifts to missing youngsters piled up at the gates of the nursery on Saturday as the tight-knit community in rural Na Klang district struggled to come to terms with the atrocity.
- Tears and contemplation -
"I have a son myself and he likes to play with toy cars, so I thought the kids killed in the attack would like this too - they were around the same age as my son," said Weerapol Sonjai, 38, told AFP after making an offering.
Before the king on Friday evening, the bereaved families knelt on the hospital floor, as is Thai custom in the presence of the monarch.
"I came here to give you my support. I am extremely sad about what happened. I share your pain, your grief," he said in a video posted online Saturday morning.
It was a very rare direct interaction with his subjects for Rama X, whose figure is sacred in the country.
The royal visit came after a day of mourning at the small, yellow-walled nativity scene, located on the edge of a village in the rural district of Na Klang, some 500km north of Bangkok.
- A rare interaction with his subjects -
Grief-stricken parents laid white roses, one by one, on the steps of the nursery where the lives of their young children were brutally cut short on Thursday afternoon.
Duenphen Srinamburi, the grandmother of one of the victims, described the horror of the attack.
"The children were sleeping. He didn't use a gun, only a knife," she told AFP.
"My grandson's face was slashed from here to here," she added, gesturing diagonally across her face. "His face was all mutilated."
A shocked mother clutches the blanket of her missing child and holds her half-filled milk bottle in her hand.
Some children were only two years old.
"I still cannot accept what happened. Assailant, what is your heart made of?", wrote on Facebook Seksan Srirach, the husband of a pregnant teacher with their child and killed at the nursery.
The former police officer armed with a legally purchased 9mm pistol and a long knife killed 36 people, including 24 children (21 boys and 3 girls), on Thursday in a murderous journey lasting around three hours which began in a nursery in the Na Klang district in the middle of the day.
The 34-year-old man then hit the road and knocked down passers-by, until he went to his home, “not far” from the nursery, according to the police. He killed his wife and their little boy there, then killed himself.
Prime Minister Prayut ordered a swift investigation into the massacre, and it emerged that Panya had been fired from the police for drug abuse.
Several people in this rural province told AFP that he was known for his methamphetamine addiction.