As noted the movie was based on a book which was written by Eleni's son Nicholas Gage (no, not that Nicholas Gage). He investigated the circumstances of his mother's death, murdered by the Communists, of course, and wrote a very moving book about it all.
In the book he describes how the children were enticed to go to Communist countries and why the parents were willing to let them go. In a time of great hunger, the Communists would line up the people of a village and offer the children a special sweet treat if they would come with them. They also promised the parents the children would be well cared for and well fed.
It was, of course, all a lie. The children were sent off to drab camps somewhere in Eastern Europe where they were maltreated while being indoctrinated in Marxist-Leninism. Gage's mother refused to let him go though he describes how badly he wanted that treat.
Later almost his entire family escaped but his mother stayed behind to be with one of his sisters who couldn't leave. Eventually his mother, an unsophisticated peasant woman, was assassinated by the Communists.
I saw the movie by chance in 1990 while in Europe. Only watched it because it was the only thing on TV that was in English (for some reason). I never forgot it.