This wasn't part of the Festival, but it is possible you saw a short film called "A Field of Buttercups". Here is a description I discovered:

A FIELD OF BUTTERCUPS - 30 Minutes
"The moving story of Dr. Janus Korczak’s devotion to his “Our Home,” an orphanage for Jewish children in the Warsaw Ghetto, during the time of the Holocaust. Based on the book by Joseph Hyams, the film portrays how Dr. Korczak chooses to remain with his 299 orphans who are marked for extermination by the Nazis, although he himself has an opportunity to leave in safety."

http://www.aldenfilms.com/holocaust.html

There is a quote from Mr. Hyams book that matches the one you related almost exactly, so I am fairly sure this is the film.

By the way, I also highly recommend the Polish film "Korczak" (1990), which is a feature length adaptation of this story.

Thank you Phil, both for the clarification and for the suggestion. The film really made an impression on me.