Russia has agreed to return four Ukrainian children to their families, as part of a deal brokered by Qatar.
The repatriation is part of a pilot scheme to return more of the thousands of children abducted by Russia following its full-scale invasion last year.
The youngest child of the four is two years old, and the oldest is 17.
Ukraine has said it identified 20,000 of its children taken by Russia.
However the number of those forcibly deported is thought to be much higher.
The International Criminal Court issued an arrest warrant for Russia's President Vladimir Putin in March, accusing him and his commissioner for children's rights Maria Lvova-Belova of the unlawful deportation of Ukrainian children.
Russia insisted that its motives were purely humanitarian, claiming it evacuated hundreds of thousands of Ukrainian children to protect them from danger, with top officials scorning the indictment at the time.
The return of the four children will test a scheme worked on by Qatar after it headed talks with Moscow and Kyiv, said a diplomat who asked to remain anonymous due to the sensitivity of the process.
It is hoped that further repatriations would follow if the first was successful, they added.
However, getting the children out of Russia has not been straightforward. In at least one case a child had to travel home via Estonia, Latvia, Lithuania and Poland.
One of the four children to be returned, a seven-year-old, was reunited with his grandmother on Friday and arrived in Ukraine on Monday.
The other three children, also reunited with their families, are expected to arrive in Ukraine later on Monday or Tuesday.
They are among thousands of Ukraine children forcibly separated from their families, Kyiv says, taken across the border into Russia and faced with an active effort to strip them of their Ukrainian identity.
The OceanNewsUK has previously found that Ukrainian children in Russia were frequently told there was nothing in their country to return to and were subjected, to varying degrees, to a "patriotic" Russian education.
In some cases Ukrainian families have been forced to make gruelling journeys into Russia to get their children back.
It is thought that so far only around 400 Ukrainian children have returned before Qatar mediated the four's return.
"They want to separate children from their biological families, Russify these children, hide these children and transfer them to another ethnic group," Daria Gerasymchuk, an adviser to the Ukrainian president for children's rights and rehabilitation previously told the OceanNewsUK.
However, work to reunite children with their families would continue, Ms Lvova-Belova said in a post on her Telegram channel, quoting President Putin as saying: "We have never been against children being reunited with their families."
Russia would also help pay transportation and accommodation costs, and where necessary carry out DNA analysis, she added.
Qatari minister Lolwah Al Khater confirmed the mediation in a statement, calling the repatriations "only a first step".
"We are encouraged by the commitment and openness shown by both sides throughout the process, which we sincerely hope will lead to more initiatives aimed at de-escalating tensions and building trust between the two parties," she added.
