DONETSK, Ukraine — Nikita, who has been living for several months with his mother and 1-year-old sister in a basement labyrinth of makeshift tents and rubber-bucket lavatories, explained why he cannot return to his toy-filled apartment.

“There is shrapnel in my bedroom,” said Nikita, 4.

About 200 refugees, 50 of them children, cower in the subterranean bomb shelter of a children’s arts center in Petrovsky district, on the far western edge of Donetsk. Three days earlier, a shell had exploded across from Nikita’s apartment, pitting the walls of his building, shattering windows and sending a fresh delivery of razor-sharp metal into his bedroom wall.

His mother, Katerina Dynya, 22, sat on a cot made from a door set atop four bricks. “We think perhaps we will let the children outside today,” she said, though the sprawling park nearby is far too dangerous. Instead, the children are allowed occasionally into an interior courtyard, where they search the rubble for shards of shrapnel.

On Friday, Ukrainian government forces and the Russian-backed separatists they are fighting in eastern Ukraine arranged a truce to allow civilians to evacuate the disputed town of Debaltseve, apparently averting a humanitarian catastrophe there. Amid a flurry of diplomatic activity on the global stage, the leaders of Germany and France traveled to Moscow to press President Vladimir V. Putin of Russia on a deal to end the war.