Wednesday's blaze at the government-run Virgen de Asuncion shelter in San Jose Pinula, near Guatemala City, has focused attention on how it was run.
Police say some residents set fire to mattresses after a riot and an escape attempt.
There have been allegations of abuse at the overcrowded centre.
At least 40 other people suffered burns in the fire, and some remain in critical condition.
President Jimmy Morales declared the country to be in official mourning. His office said the cause of the fire was being investigated.
The tragedy was "a great shame for the state and for the whole world", Supreme Court Magistrate Maria Eugenia Morales told reporters.
Grieving relatives of victims and distraught families waiting for news have been gathering outside the home, where police intervened after a riot broke out on Tuesday evening.
Many children escaped at the time.
A group of youths isolated by authorities after the riot caused the blaze by setting fire to mattresses, police chief Nery Ramos said.
Firefighters said it appeared to have started in the female section of the shelter.
Guatemalan media report that the riot erupted due to alleged sexual abuse by staff and frustration with the poor conditions and food.
"It was a ticking time bomb. This was to be expected," a former employee, Angel Cardenas told the AFP news agency.
Open-living arrangements meant that "girls who simply were suffering, that didn't have any problems with the law, are mixed with young people who have committed crimes", presidential spokesman Heinz Heimann said.
"This can't be allowed to continue."
All those who died were aged between 14 and 17. The fire ripped through the facility in minutes.
After the blaze, images showed burned bodies covered by blankets lying in one of the blackened rooms. Many of those injured have second- and third-degree burns, and some are in critical condition, hospital officials say.
The shelter, run by the social welfare ministry, takes in children up to the age of 18 who have suffered abuse or have been abandoned.
But local media say the shelter was also functioning as a juvenile detention centre, to which judges were sending adolescents involved in criminal cases.
The UN children's fund in Guatemala said on Twitter it "condemns the tragedy", adding: "These children and adolescents must be protected".
Reports say the capacity of the home is 400, but that many more children were living there at the time.