Fulla, a nickname given to 10-year-old Afnan, was the eldest. All three were from the Shuheiber family, in Gaza City's Sabra district.
After being cooped up at home for days on end, neighbors said the children were taking advantage of the relative calm that followed a brief truce between Israel and Hamas.
"They were playing on the roof," said neighbor Raed al-Kurdi, 33, his white vest stained with blood.
"We were sitting on our roof next to our neighbor's one and we found all of a sudden a rocket coming from above and it hit their roof," he added.
"The people who were injured were from the Shuheiber family, there were children, two girls, two boys and two grown men.
"They were in serious condition, we carried them out in our arms."
Three of the children died en route to the Shifa hospital, where they were laid out on steel tables in the morgue as doctors in blue coats moved around them, cleaning them.
Each had coin-sized pieces of flesh gouged out from their limbs by shrapnel.
Next to them, their uncle Mohamed wept openly.
An employee at the hospital, he heard the call go out for ambulances after the strike that hit the Shuheiber home.
"They were children, just playing on the roof. And now they're dead, lying in front of us," he said, his voice anguished but also angry.
"How can this be, how can this be?"
The morgue chief asked the distraught family members if they want to allow media waiting outside into the room.
"It is up to you, but if you want to show the world what happened here, we will let them in," he told Mohamed and other relatives inside, who assented tearfully.
The three children were lined up beside each other, along with a fourth child brought in from an earlier strike in Gaza City.
Fulla was laid in the middle and her cousins one on either side.
Her curly hair framed her face, specked with blood.
Her T-shirt might once have been white, but now it was completely red, soaked through with her blood.
To her right was 8-year-old Jihad, his turquoise T-shirt and trousers torn through by shrapnel.
To her left was Wissam, seven years old, his eyes still open as through he was staring into the middle distance.
His trousers had been removed, revealing his blue and yellow superhero underwear.
GAZA CITY (AFP) -- Brothers Jihad and Wissam were playing on the roof of their Gaza apartment with their cousin Fulla, when an Israeli strike came from the blue skies above and killed them.