The Youngest Faces in the Ukrainian Conflict 10 months of conflict claimed thousands of lives, shattered countless others.

DONETSK, Ukraine -- The cease-fire that went in effect in eastern Ukraine today may quiet the guns, but the echoes of 10 months of bombardment will likely ring in the ears of the child survivors of the conflict for the rest of their lives.

Just hours before the fighting was supposed to stop, Ekaterina and her 8-year-old brother Ivan played on a slide and jungle gym in a central park of Donetsk with the sound of heavy bombardment raining down around them.

But the two children, who had only left their basement shelter Saturday for some sunshine and fresh air as their mother went to buy food, ignored the explosions.

Ekaterina, who is just 5 years old, even explained that she could tell the difference between mortars, rockets, and other artillery by the sounds they made as they hit the ground.

In 15 minutes, 25 explosions were heard, even though it was just hours before an internationally sponsored ceasefire was to go into effect between Ukrainians and Russian-backed separatists in a conflict that has killed about 5,500 people.

For some, the pause in fighting came too late. The last few days, which saw increased shelling as both sides tried to lock in advantageous positions before the midnight deadline, were deadly for civilians -- adults and children alike.

While missiles fell close to the park where Ekaterina and her brother played, they also landed nearby where Alexander Zakharchenko, the rebel leader of the self-styled Donetsk People's Republic (DNR), was about to hold a news conference. Four shells that missed his headquarters killed three civilians and injured five.

Elsewhere, in the rebel-held town of Gorlovka, three children were killed as they took a bath at home, the building hit by shells fired by forces supporting the Ukrainian government.

In the city of Artemovsk, a 7-year-old was killed by fire from pro-Russian separatists.

Almost everybody hopes the ceasefire will hold, but few believe in it.

Zacharchenko said he had no intention of ceasing to fight in the "internal regions of the DNR," including Debaltsevo, a railway junction town where Ukrainian forces are surrounded by the rebels.

"Any attempt to break out of Debaltsevo will be stopped by us," he said.

Ukrainian President Petro Poroshenko warned that if separatists do not abide by the ceasefire, he will impose martial law throughout Ukraine's territory, his spokesman told ABC News.