Toddlers to teenagers are sleeping in classrooms at the prestigious Institution Saint-Louis de Gonzague.
A severe wave of violence erupted between two rival gangs in the Cité Soleil area on 7 July.
Around 300 people have reportedly been killed, Human Rights Watch says.
Children joked around in the playground on Friday, playing hide and seek or improvised football games with plastic bottles, Reuters reported from inside the school.
But Sister Rosemiline, a nun with religious community group Kizito Family, said “the kids need a lot of help”.
“The situation is really bad where they are from. We are waiting for food but what we get is not satisfactory to the kids,” she said, adding that she is hoping to relocate them.
A community organiser told Reuters that the children wore school uniforms to convince gang leaders they were on their way to class in order to escape the violence.
Most of the children are alone as their parents were unable to flee the Cité Soleil turf war, he said.
Battles between the G9 and G-Pèp gangs erupted on 7 July over control of the neighbourhood.
Human Rights Watch said on Friday that roughly 300 people have been killed, including 21 whose bodies were apparently burned, and 16 people have been reported missing, citing the National Human Rights Defence Network.
“The gangs also burned homes and used heavy machinery to demolish them, the group said, with 125 homes reportedly destroyed,” it said.
The situation has become so dire that earlier this week the UN Security Council voted unanimously to ban some weapon sales to Haiti.
Gang violence has shot up since the assassination of President Jovenel Moïse by mercenaries a year ago.
According to the UN Integrated Office in Haiti, 540 people were kidnapped and more than 780 were killed between January and May 2022. In the last five months of last year, 396 people were kidnapped and 668 killed.
The country has also been hit by chronic fuel and electricity shortages because of the gang violence.
