After a nearly two-hour stay in Ukraine, Biden’s motorcade then returned to Slovakia.
The U.S. first lady has been visiting Eastern Europe, meeting with U.S. troops and Ukrainian refugees.
Earlier on Sunday, she met volunteers helping refugees in Slovakia and visited another school where children were making crafts for Mother’s Day.
“The hearts of the American people are with the mother of Ukraine,” Biden told the gathering.
Classrooms are packed with families whose husbands and fathers stayed in Ukraine to fight the war.
One woman told a pool reporter traveling with Biden that the first lady’s visit was encouraging.
“It means support for us,” the woman said. “We’re tired. It’s emotional support for us.”
In recent weeks, a number of U.S. officials have visited Ukraine in solidarity, including Secretary of State Anthony Blinken, Secretary of Defense Lloyd Austin and Speaker Nancy Pelosi.
Also visiting the troubled country on Sunday was Canadian Prime Minister Justin Trudeau, who met with President Zelensky in Kyiv, and U2 starring Bono and the Edge, He performed in a train station in the capital.
But there was more bloodshed on Sunday when a school where civilians had taken refuge in the village of Bilokhorivka in eastern Ukraine was bombed.
As many as 60 people may have died, a district official said.
“We long ago accused the Russians of war crimes, and that’s what caused that,” U.S. ambassador to the United Nations Linda Thomas-Greenfield told CNN of the bombing. “We will continue to work with Ukraine. Prosecutors and others are working together to document evidence of their war crimes so they can be held accountable. This just adds to the long list we already have.”