Several U.S. lawmakers warned on Wednesday that the repatriation of the roughly 20,000 Ukrainian children whom Russian troops have forcibly abducted should be a nonnegotiable part of discussions to end the war.

Russia’s military has forcibly taken an unspecified number of Ukrainian children, deported them to various parts of Russia or Russian-occupied Ukraine, and then inundated them with anti-Ukrainian propaganda with the intent of destroying an entire generation of Ukrainians.