Taoiseach Simon Harris has described Russia’s forced displacement of thousands of Ukrainian children as "morally repugnant".
Mr Harris was speaking at the start of a two-day summit at the Burgenstock in Switzerland, in a bid to start a peace process to end the war in Ukraine.
More than 90 countries have sent high-ranking delegations to the summit.
US Vice President Kamala Harris announced more than $1.5 billion (€1.4 billion) in energy and humanitarian aid for Ukraine, where infrastructure has been struck by Russian airstrikes since the 2022 invasion.
Since the start of Russia’s full-scale invasion of Ukraine in February 2022, thousands of Ukrainian children have been illegally moved to Russia or Russian-occupied territories in Ukraine.
"We estimate that around 20,000 children have been snatched from their families, from their communities, their country and been moved to Russia or occupied territories within Ukraine," Mr Harris said.
The Taoiseach said that he was "utterly appalled and sickened by what’s happening to Ukrainian children".
He added: "When did it ever become acceptable for children to be used as a weapon of war.
"I want to major on this point in terms of what more the world can do to apply pressure to Russia in relation to this."
The Taoiseach also took part in discussions on humanitarian aspects of the conflict and, speaking to RTÉ News, emphasised Ireland’s role in helping Ukraine to de-mine parts of the country.
In February, Ireland sent de-mining equipment to Ukraine and Irish defence personnel have trained Ukrainian troops on operating the de-mining units in Poland.
The Taoiseach also said that this weekend’s summit was about "trying to find common ground and trying to create a consensus approach to a number of issues".
Those issues include food security, nuclear safety and humanitarian dimensions to the conflict such as prisoner exchanges and the repatriation of Ukrainian children.
The UN Charter, said Mr Harris, and the territorial integrity of Ukraine are "absolutely key to any peaceful settlement".
During the summit, Mr Harris also held talks with several world leaders on the margins of the event including Belgian Prime Minister Alexander De Croo, the US Vice President, French President Emmanuel Macron, Dutch Prime Minister Mark Rutte and Canadian Prime Minister Justin Trudeau alongside a discussion with British Prime Minister Rishi Sunak.
The Taoiseach also discussed Palestine with Spanish Prime Minister Pedro Sanchez and Prime Minister of Norway Jonas Gahr Støre after all three nations recognised the State of Palestine last month.
